Introduction

The global market for cosmetic products is growing relentlessly where Brazil ranks third in this market and second for haircare products (Crippa et al. 2015). The procedure called “progressive blow-dry” is performed using products called hair straighteners whose purpose is to straighten, smooth, and reduce volume of the hair and is applied by a professional hairdresser.

The addition of formaldehyde to the cosmetics used for hair smoothing is permitted in Brazil at concentrations limited to 0.2%, as stipulated by the National Health Surveillance Agency (ANVISA), the regulatory body responsible for these products in Brazil. With regard to professional hairdressers, Regulation no. 3,214 of 8 of June 1978 by the Ministry of Labor and Employment (MTE) approves the standards governing occupational safety and health in Brazil through standard no. 15 (NR15) which rules on the execution of hazardous activities and operations according to the nature and duration of exposure to chemical agents and that will not be harmful to workers’ health during their working lives. This standard establishes the maximum allowed limit of exposure to formaldehyde at 1.6 ppm (or 2.3 mg/m3 of air) for a working week of up to 48 h, although the prevailing rule is out of date, in that the standard working week in Brazil is currently 40 h.

Despite this regulatory framework, the illegal use of formaldehyde in hair smoothing products persists in Brazil. Recently, there has been intense debate over the toxicity of formaldehyde and its carcinogenic potential, raising major concerns in organizations responsible for occupational safety and toxicology, and formaldehyde is considered carcinogenic by the WHO (World Health Organization). Therefore, concentrations above legal limits in products for cosmetic use pose serious exposure risks to both professional workers and clients. Exposure to this chemical poses a significant potential risk due to its toxicity to the body, including respiratory tract toxicity, causing a decrease in lung function even if the exposure is in low concentrations and may develop an abnormal reaction in the tissues of exposed professionals inhalation or dermal absorption leading to upper and lower respiratory problems, including asthma (Dahlgren and Talbott 2017). According to the International Agency for Research on Cancer (IARC), formaldehyde is considered carcinogenic to humans and is classified as group I (IARC 2006; Kupczewska-Dobecka 2007; NTP 2011; Mundt et al. 2017). The classification of carcinogenicity of formaldehyde is based on the evidence that this substance has carcinogenicity potential for the respiratory and hematological systems, such as sinus, nasopharyngeal, and myeloid leukemia in humans, respectively. This is due to the physicochemical characteristics of formaldehyde, such as the high solubility of this gas in water. During respiration, an important part of the formaldehyde is absorbed by the nasal mucosa causing irritation of the nose, larynx, and pharynx (Andersen and Proctor 1982; Lorenzini 2012). In 1993, the National Cancer Research Agency (IARC) evaluated a number of human and animal studies on the carcinogenicity of hair dyes and concluded that work in salons involves potentially carcinogenic exposures (IARC 1993).

The US Occupational Safety and Health Administration (OSHA) stipulates an average exposure limit for an 8-h work shift of 0.75 ppm (OSHA 2011; NIOSH 1994). For concentrations above 2.0 ppm, it is recommended that exposure time not exceed 15 min (short-term exposure limit or OSHA-STEL). Hairdressers constitute the main professional group potentially exposed to formaldehyde through handling of hair straightening creams and products, with 628,110 such professionals registered in Brazil (SEBRAE 2017). This represents a large contingent of individuals that work with beauty and cosmetic products that are exposed to these chemical agents. Thus, studies quantifying the exposure of hairdressers to formaldehyde during work shifts and the risks associated with this chemical are of social and scientific importance, yet existing studies are fragmented and address only isolated aspects of hairdresser exposure.

Against this background, the objective of the present study was to carry out an assessment of the exposure of professional hairdressers to formaldehyde, considering the different variables that impact the intensity of exposure, thereby helping to protect workers’ health. The primary objective of this study was to quantify, via air tests, the occupational exposure of hairdressers to formaldehyde at two timepoints: during the most critical 15-min period of the hair straightening procedure and during the 8-h work shift. The data collected were compared against the exposure limits stipulated in Brazilian (NR15) and North American (US OSHA and US NIOSH) standards, associated with a range of variables: physical structure of the salons studied, socioeconomic profile of clients, work processes, and quantitative assessment of the formaldehyde content in the formulations of the hair smoothing products used, comparing these against exposure levels.

Materials and method

Selection of beauty salons

The beauty salons were selected based on the data provided by the Municipal Health Secretariat of Bauru city, São Paulo state, Brazil. A total of 144 salons registered in the city were analyzed. Salons were stratified according to the classification of the Índice Paulista de Vulnerabilidade Social (IPVS) – Paulista Social Vulnerability Index—developed by the Seade Foundation (SEADE Foundation 2010). This indicator defines, using 6 different groups, the characteristics of the living conditions of populations vulnerable to poverty (Fig. 1).

Fig. 1
figure 1

Location of salons randomly selected according to the Índice Paulista de Vulnerabilidade Social- Paulista Social Vulnerability Index (IPVS), Bauru 2017–2018

Full size image

Study population

This study included 23 beauty salons, randomly selected from the 42 visited in the city of Bauru (São Paulo, Brazil). The hairdressers recruited all signed the free and informed consent form before participating in the study and were aged older than 18 years. The study procedures were carried out after a meeting with the employees of each participating salon, during which the aims of the study were explained and all queries addressed.

Questionnaire

The professionals interviewed were hairdressers and assistants who performed the hair straightening procedure. Interviewees completed two structured questionnaires. The first questionnaire collected personal details and demographic and professional data, including age, sex, place of work, and health problems of participants. Habits related to length of exposure (estimated by time working in the sector of the salon where the individual is currently exposed) and use of products and materials for performing hair straightening and personal protective equipment (PPE). The second questionnaire was filled out by the researcher while the hair straightening procedure was being carried out. Information was collected on work processes, PPE use, salon physical structure, use of air ventilation systems, and possible exposure of other professionals in the beauty salon team. All details of the work process during the 8-h work shift at the beauty salon were recorded, as per guidelines of the American Industrial Hygiene Association (AIHA 2015).

Formaldehyde sample collection

Samples were collected by inhaled air testing at two timepoints: the working day on which the hair straightening procedure was carried out and the working day on which the procedure was not performed (control day), adopting the method outlined below:

  1. 1.

    Active sampling: inhaled formaldehyde vapor samples were collected for the 15-min period from commencement of the hair straightening with the product (15-min short-term exposure limit) using a portable personal sampling pump by the soap bubble method equipped with a collection system of tubing containing silica gel treated with 2,4-dinitrophenylhydrazine (DNPH) (Fig. 2) attached to the hairdresser, with the device oriented toward the personal breathing zone, within a 50 ± 150-mm radius of the nostrils.

Fig. 2
figure 2

Placement of sampling pump and UMEX sampler on professional during hair straightening procedure

Full size image

The samples were collected at an air flow rate of 0.9 L/min (NIOSH 2016). The sampling pump was calibrated according to the technical standard established by the Occupational Hygiene Standard (Pastorello and Pinto 2002) before and after sample collection. The tubes were sealed immediately after each sampling event and sent for laboratory analysis within 7 (seven) days of collection.

  1. 2.

    Passive sampling: performed during the 8-h work shift, using a UMEX 100 passive sampler (SKC Inc., Eighty Four, USA), according to EU ISO 16000-4-2004 for determination of formaldehyde levels in the air of the salon environment. This sampler was also placed on the professional at the height of the personal breathing z\one, where it remained throughout the 8-h work shift. After collection, the UMEX 100 SKC sampler was sealed, placed in an aluminized pouch, and sent for laboratory analysis.

Collection and preparation of cosmetic cream samples

The samples of the cosmetic creams applied to client hair were collected during the hair straightening procedure and placed in amber glass flasks and refrigerated at 4 °C. Sample preparation involved weighing the creams in 10-mL volumetric flasks followed by dissolution in ultrapure water. Dinitrophenylhydrazine (DNPH) and acetonitrile were then added to the flask and the remaining volume made up with ultrapure water. The solution was derivatized in a dark place for subsequent filtration through a 0.45-μm PTFE filter and analyzed using high-performance liquid chromatography (HPLC).

Preparation of vapor samples for HPLC analysis

The samples collected by the active sampler were prepared by eluting 10 mL of acetonitrile. This solution was transferred to the 10-mL flask and the volume completed with solvent. The resultant solution was then filtered through a 0.45-μm PTFE filter and analyzed by HPLC.

The vapor samples contained in the passive UMEX sampler were prepared according to the technical protocol UMEX Passive Sampler for Formaldehyde Cat. No. 500-100 by adding 3 mL of acetonitrile to each of the tapes inside the sampler, followed by manual shaking for 1 min. The solution was then filtered in a syringe filter with a 0.45-μm Teflon (PTFE) membrane and analyzed by HPLC.

The formaldehyde DNPH derivative was dissolved using 3.0 mL of acetonitrile in a 4-mL glass flask for later detection and quantification by HPLC with spectrophotometric UV-Vis detection at a wavelength of 365 nm. A reverse-phase C-18 column was used and the mobile phase was water and acetonitrile on a isocratic elution program. The filter used as a blank was similarly desorbed and analyzed. The certified reference material was used for quality control of the analyses (MDL number MFCD00191364).

The chemical analyses were performed at the Chemical Analyses Laboratory of the Brazilian Institute for Technological Research (IPT), São Paulo, Brazil.

Formaldehyde analysis methods

Analysis of the formaldehyde vapors collected was performed using three analysis methods:

  1. 1.

    Method developed by the Chemical Analyses Laboratory of the IPT (Brazilian Institute for Technological Research) applied for the analysis of both samplers (active and passive). All the samples were submitted to an extraction process for analysis in liquid state, solubilized, and filtered using a closed flask to prevent volatilization of the formaldehyde. The solutions were analyzed by HPLC.

  2. 2.

    Method NIOSH 2016 - Manual of analytical methods (NMAM), fourth edition, applied to the samplers of the adsorbent tube type using silica gel treated with dinitrophenylhydrazine (DNPH) and hydrochloric acid, connected to a suction pump, collecting formaldehyde vapors.

  3. 3.

    Method UMEX 100 passive sampler for formaldehyde attached to the professional to detect low levels of formaldehyde. The UMEX 100 contains a tape treated with DNPH. Sampling rates can be validated from 15 to 24 h or 7 days. Analysis is performed by HPLC.

Data processing and statistical analyses

The values obtained for formaldehyde concentrations in the samples and the data from the questionnaire were input and codified in an Excel (Windows) spreadsheet database. Statistical analysis was carried out using the Stata 13 software. Data analysis included descriptive statistics, expressed as absolute and relative frequencies, and the following tests: chi-square, Pearson’s correlation coefficient, analysis of variance (ANOVA), and Student’s t test. A 5% level of significance was adopted.

Results

Results obtained on active and passive sampling

The results obtained on active and passive sampling were analyzed using the specific method for each sample type and then compared with the tolerance limits defined in Brazil (NR15) and in the US (OSHA) standards.

The active samples yielded different formaldehyde concentrations for each analysis method. Using the NIOSH method, concentrations ranged from 0.00 to 4.12 ppm. According to the tolerance limit defined by NR 15 of 1.6 ppm, using the NIOSH method, 7 salons (30% of samples) exceeded this limit. For the IPT method, this tolerance limit was exceeded by 9 salons (39% of samples), where the concentrations obtained using this method ranged from 0.00 to 4.17 ppm. Based on the formaldehyde concentration limit of 2.0 ppm established by the OSHA: using the NIOSH method, 4 salons had formaldehyde concentrations above the limit (17% of samples), whereas according to the IPT method 7 salons had above permitted levels (30% of samples).

For the passive samples, formaldehyde vapor concentrations ranged from 0.06 to 1.92 ppm according to the UMEX method. Using the IPT method, values ranged from 0.07 to 1.79 ppm. Three salons had levels above the limit defined for passive samples by the OSHA standard of 0.75 ppm for an 8-h work shift.

The concentrations detected for each method are depicted in Graphs 1 and 2.

Graph 1
figure 3

Formaldehyde levels (ppm) on active sampling (NIOSH 2016), by beauty salon, Bauru, 2017–2018

Full size image
Graph 2
figure 4

Formaldehyde levels (ppm) on passive sampling (UMEX 100 method passive sampler for formaldehyde Cat No. 500-100), by beauty salon, Bauru, 2017–2018

Full size image

The results on the analyses of formaldehyde vapor concentrations at different points in the procedure were assessed based on the mean concentrations obtained. Comparison of levels during the first 15 min period of the procedure with those on the control day (procedure not performed) revealed a statistically significant difference (p < 0.0005). Mean concentrations were 1.32 and 1.41 ppm for the NIOSH and IPT methods, respectively.

Regarding the passive samples, during the 8-h work shift, mean residual formaldehyde concentration was 0.40 ppm on hair straightening day versus 0.04 and 0.05 ppm on the control day (no hair straightening), using the IPT and UMEX methods, respectively.

Results of hair smoothing cream analysis

Regarding the formaldehyde concentrations contained in the creams used for hair smoothing, the 23 Brazilian brands assessed greatly exceeded the 0.2% limit established by ANVISA. The concentrations obtained ranged from 3 to 11%, representing 18 to 54 times permitted levels.

Characteristics of beauty salons and work processes

The physical infrastructure of the salons assessed and their relationship with exposure had no statistically significant influence (p > 0.05) on the results of the formaldehyde concentrations for maximal 15-min and 8-h work shift exposures.

Regarding occupational exposure to formaldehyde and the infrastructure-related variables of the workspace, there was a moderate positive correlation (r = 0.4–0.7) between formaldehyde concentrations determined by passive sampling (using UMEX 100 and IPT calculations) and ceiling height (range 2.33 m to 5.89 m), and also with the size of the workspace where the procedure was performed. These correlations were statistically significant (p < 0.05).

Table 1 compares the physical characteristics of the beauty salons and the formaldehyde concentrations obtained in samples:

Table 1 Comparison between the physical characteristics of the beauty salons and the formaldehyde concentrations obtained in samples
Full size table

Salon 4 had the lowest formaldehyde concentrations during the hair straightening procedure: active sample of 0.00 ppm on the two methods assessed and passive sample of 0.10 ppm by the UMEX method and 0.11 ppm by the IPT method. The door was left open during the execution of the procedure, and also throughout the 8-h work shift.

Salon 22 registered the highest formaldehyde concentrations during the hair straightening procedure: active sample of 4.12 ppm by the NIOSH method and 4.17 ppm on the IPT method, passive sample of 0.51 ppm by the UMEX method and 0.48 ppm by the IPT method. During execution of the procedure, the doors and windows were kept closed and 2 (two) fans were used.

With regard to the air-conditioned workspaces, such as salon 21, formaldehyde concentrations obtained by active sampling, during the straightening procedure, were 1.08 ppm and 1.09 ppm, by the NIOSH and IPT methods, respectively. The assessment of passive sampling for the 8-h work shift yielded concentrations of 0.25 ppm and 0.23 ppm by the UMEX and IPT methods, respectively. The salon doors were kept closed during the procedure and the 8-h work shift. There was no window and the door opening measured 1.80 m.

At salon 2, the hair straightening procedure was carried out with the doors and windows open, and likewise throughout the 8-h work shift. Formaldehyde levels measured during the procedure were 0.42 ppm and 0.56 ppm by the NIOSH and IPT methods, respectively. The assessment during the 8-h work shift revealed formaldehyde levels of 0.55 ppm and 0.51 ppm, by the UMEX and IPT methods, respectively. The use of 1 (one) fan was noted during the study. In this salon, the formaldehyde concentration in the straightening cream was 10.96%, representing the highest level found among the 23 salons analyzed (Fig. 3).

Fig. 3
figure 5

Physical structure of salons 4, 22, 21, and 2

Full size image

Although not reaching statistical significance, a negative correlation was found between door/window openings and formaldehyde concentration in the air, i.e., the greater the door and window openings, the lower the formaldehyde concentration in the workspace sampled. The ceiling height and size of the workspace were also positively correlated with formaldehyde concentrations in the passive sample (ceiling height: r = 0.45 and p = 0.03 and size of workspace: r = 0.63 and p = 0.01), i.e., the greater the ceiling height and larger the workspace in which the straightening procedure was carried out, the higher the formaldehyde concentration. This result was unexpected, but should be assessed in the context of other salon characteristics, which also influence formaldehyde level in the zone of respiration of the hairdresser, such as window opening, general dilution ventilation, and hair washing.

Airflow velocities had no statistically significant effect (p = 0.05), owing to the other variables related to the physical characteristics of the salons. The work shift averaged 9.1 h, 5 days a week, almost 2 h of which was dedicated to performing hair straightening procedures.

Concerning work processes, the procedures and care for applying the product were not standardized in terms of sequential instructions of the processes or frequency of execution. The application and handling of the product were performed according to the directions carried on labels and to instructions given by the sales representative. The products were applied by a hairdresser in 82.6% of cases (group with highest potential of exposure) and in 17.3% by assistants. Both these groups were aged 20–64 years, comprising 86.96% female and 14.04% male.

Of the 23 salons assessed, 13 professionals reported that they washed the client’s hair before performing the flat-ironing hair smoothing treatment process. In these salons, the formaldehyde concentrations during the hair smoothing process were 2.94 ppm by the NIOSH method and up to 2.96 ppm by the IPT method. By contrast, the 10 salons that did not wash hair or washed upon client request had formaldehyde levels of up to 4.12 ppm by the NIOSH method and 4.17 ppm by the IPT method, almost double the level of salons that washed client hair.

The use of personal protective equipment (PPE) occurred in 95.6% of the salons, defined as use of at least one of the following items of PPE: mask, gloves, aprons, and splash goggles. One of the hairdressers was pregnant while carrying out the straightening procedure during the assessments phase and three employees reported previous miscarriages, including repeated events. The work-related health problems reported by 65.22% of professionals interviewed were eye irritation, skin lesion, headache, upper and lower limb pain, and respiratory problems.

Comparison of results for the Paulista Social Vulnerability Index (IPVS)

With regard to social vulnerability (IPVS) of the site of the beauty salon, significant differences (p = 0.045) only in formaldehyde concentrations of the cream used were noted, where salons situated in microareas with IPVS 3 (stratus B) had higher concentrations of formaldehyde in the smoothing creams compared with the other microareas.

For the active samples, the mean formaldehyde concentrations during the straightening procedure ranged from 1.04 to 1.43 ppm on the NIOSH method and 1.01 to 1.60 ppm by the IPT method. The salons classified as IPVS 1-2 had the highest mean formaldehyde concentrations by the NIOSH method (1.43 ppm), whereas the salons classified as IPVS 3 had a mean level of 1.60 ppm by the IPT method. This mean was 18% higher by the NIOSH method and 22% higher by the IPT method than for salons situated in other microareas. Regarding the passive samples, on days of the straightening procedure, mean formaldehyde concentrations during the 8-h work shift ranged from 0.39 to 0.50 ppm by the UMEX method and 0.17 to 0.47 by the IPT method, where the highest means were in salons classified as IPVS 1-2, measured by both the UMEX and IPT methods.

On the control day, when no straightening procedures were carried out, mean formaldehyde levels for the 8-h work shift were 0.02 to 0.05 ppm by the UMEX method and 0.01 to 0.04 by the IPT method. The highest concentrations can be seen in salons with IPVS 1-2 for both analysis methods.

Discussion

Taken together, the study results show that hairdressers are exposed to high concentrations of formaldehyde when performing the hair straightening procedure (progressive blow-dry). This issue is especially alarming considering that 86.96% of interviewees were female professionals of fertile age (20–45 years old) and that the chemical analyzed is carcinogenic (IARC 2012a, b, c).

Two exposure situations were assessed: the most critical 15-min period of the procedure, measured by active sampling, during the blow-drying and flat ironing stages with greatest production of vapors, and the 8-h work shift, measuring the exposure to residual formaldehyde vapors and to chemical products used in the beauty salon. During the collection of samples for the present study, 82.61% of professionals were found to use only protective gloves while performing hair straightening. The remaining professionals used only a procedure mask, without a suitable filter to protect against formaldehyde inhalation.

The work processes adopted were associated with major differences in formaldehyde concentrations, as measured by the two methods employed in the sample analyses. Of the 23 salons assessed using the NIOSH method, 30% exceeded the formaldehyde limit of 1.6 ppm stipulated by NR 15 (Ministério do Trabalho 1997), while 39% of samples were above this limit measured by the IPT method. Based on the formaldehyde limit determined by the OSHA of 2.0 ppm, concentrations at 17% of salons exceeded permitted levels on the NIOSH method. Levels in samples measured by the IPT method were above permitted limits for 30% of salons. Notably, in those salons with formaldehyde concentrations above exposure limits, hair washing was not performed prior to flat ironing. Salons with lower formaldehyde concentrations performed hair washing before completing the other stages of the process, thereby reducing exposure to formaldehyde. Based on this data, it can be concluded that hair washing to remove excess product prior to blow-drying and flat ironing reduced the exposure of the professionals to formaldehyde. No statistically significant difference was found, probably owing to the small number of salons assessed, a factor recognized as a limitation of this study.

Some variables related to hairdresser exposure during the application of hair straighteners include the amount of product used, the length of time for each step of the procedure, various product applications, salon size, and type of ventilation. Some variations may occur by certain methods of applying products used by a particular professional. One or two sample results below a set limit do not automatically guarantee that the product cannot result in exposures above these limits (Oregon OSHA 2010).

According to the publication of INCA (2012) on the relationship between professions and cancer, formaldehyde ranks among the main groups of cancerous agents associated with work, where its absorption via respiratory, oral, and cutaneous routes, together with the duration and frequency of exposure, influences toxicity and can be considered risk factors for some types of cancer.

Another important aspect assessed in this study is the illegal use of hair smoothing products whose product formulation contains formaldehyde levels above the 0.2% limit permitted by the ANVISA. The samples of straightening creams collected for a range of brands produced by different manufacturers in Brazil were submitted to laboratory analyses, revealing high levels of formaldehyde in their formulations ranging from 3 to 11%, i.e., concentrations up to 54 times above the limit prescribed in RDC no. 36 of 2009 by the ANVISA. Crippa et al. (2015) analyzed formaldehyde samples in 10 brands of the products most commonly used in beauty salons in Brazil and found that 80% contained levels above those recommended by ANVISA. In another study conducted by Abreu et al. (2015) to determine formaldehyde levels in commercial formulations of permanent and progressive hair smoothing products, results indicated formaldehyde concentrations 19.15 times higher than the levels allowed by the regulatory agency.

In the study by Pierce et al. (2011), a simulation of exposure to formaldehyde was performed to characterize potential exposures of salon and client workers during treatments with smoothing products of four different brands. In the short term (6–16 min), analyzes of formaldehyde concentrations were on average 2.35 and 1.11 ppm, higher than the concentrations initially reported by the NIOSH and Oregon OSHA (during the drying stroke: 0.84 and 0.41 ppm, respectively). Similarly, the long-term (41–371 min) concentrations in each treatment performed during the 8-h workday were 1.19 to 0.16 ppm, above the average concentrations obtained by Oregon OSHA over the same period: 0.447 and 0.078 ppm. The reasons for this discrepancy are unclear, but may be related to consecutive procedures performed throughout the study day (unlike NIOSH and Oregon OSHA “individual treatment” studies), or a number of other factors, including differences air exchange rates, room dimensions, application techniques, and so on.

The study results showed that, although the straightening creams contained above permitted formaldehyde levels, the fact that the creams had more formaldehyde did not translate to a commensurately higher exposure for the hairdresser. Hair washing, for example, reduced this exposure, as did the use of ventilation systems, although the difference was not statistically significant.

It is noteworthy that, with respect to the work processes practiced by these professionals, lack of formal professional technical training, awareness about biosafety procedures, sustainable production processes, and standardizing of the services were identified by the Brazilian Micro and Small-Business Support Service (SEBRAE 2016a, b, c) as shortcomings of this rapidly growing market in Brazil.

The beauty salons categorized according to the IPVS were assessed by the NIOSH method and the three strata of social vulnerability of the respective address were compared, irrespective of the economic status of the beauty salon. The results showed no significant difference in exposure of the hairdressers with respect to the social vulnerability of the address of the salon. In the present study, the more affordable down-market salons were not those located in areas of greater social vulnerability, but instead situated in inner city regions of Bauru with a high flow of people due to local popular businesses. This fact indicates there was no significant association between greater exposure to formaldehyde and higher social vulnerability of the address where the salon was located. The fact that the salon was situated in a poorer or wealthier area had no influence on hairdresser exposure, indicating that the main impact of exposure stemmed from the work processes adopted. The prices charged at the beauty salons located in the city center (IPVS 3) were often lower than rates charged for the same procedure by salons in regions with higher social vulnerability index. This phenomenon was associated with significantly higher formaldehyde concentrations in straightening creams used in IPVS 3 salons.

With regard to the structural characteristics of the salons studied, parameters included size of the workspace in which the progressive blow-dry procedure was performed, the number and size of doorways and windows, and the use of natural or artificial ventilation. Surprisingly, the size of the workspace influenced exposure but had the opposite effect to that expected. Salons with a high ceiling (range 2.23 to 5.89 m), showed a positive correlation with passive sampler formaldehyde concentrations. This finding might be explained by the fact that exposure control is multi-factorial; other variables can also influence exposure to formaldehyde, such as keeping windows and doors closed while carrying out hair straightening and low use of ventilation systems and/or use of air-conditioning. The small number of salons assessed in the present study precluded the treatment of data with multiple regression analysis, where this might have confirmed the hypothesis.

The European Agency for Safety and Health at Work (2014) reveals that adequate ventilation of salons is vital to reduce exposure. A study conducted in France showed that the majority of hair salons did not have effective ventilation systems for removing pollutants, rendering the professionals exposed to inhalation of toxic vapors and/or irritant sensitizers and susceptible to respiratory diseases, where a high prevalence of occupational asthma was found (Maraschin 2009).

According to the INCA (2012), the main factor influencing toxicity for the situation of exposure to a specific chemical is exposure intensity, which depends, among other factors, on the concentration of the toxic agent in the workplace, work type and intensity, length of daily exposure throughout professional life, frequency of worker exposure, and the environmental conditions (temperatures, humidity and ventilation). The INCA also suggests that exposure estimates be respected and treated as a target for reduction and organized intervention, guided by central organs of occupational health surveillance and by cancer registries based on notification systems for work-related cancer.

A recently published study evaluated the exposure of hairdressers to formaldehyde in beauty salons during the use of straightening products and the consequent association of this exposure with biomarkers of genotoxicity. There was a difference in the urinary concentration of formic acid when compared with the start and end of the work shift, with the concentration of biomarkers positively associated with environmental formaldehyde concentrations (Peteffi et al. 2016).

Despite the epidemiological findings, the association between the profession of hairdressing and human malignancies, with no increase in DNA strand breaks (SCGE) or sibling exchange test in peripheral lymphocytes, a mutagenic urine activity, was found in a population of 15 hairdressers strongly exposed who had an extensive history of work without protective measures (Sardas et al. 1997; Galiotte et al. 2008).

Hairdressers are exposed to formaldehyde through handling of hair smoothing creams and products. Many chronic diseases stem from the human genome and the totality of human exposures throughout the course of life. These exposures can be via general external environmental factors, specific external factors or internal factors, from conception to the end of life, and is referred to as the exposome (Siroux et al. 2016; Rappaport et al. 2014). This study focused on a specific external exposure factor of the human exposome, namely occupation, which can have a major impact on the human exposome, as the study results illustrate.

Conclusions

The results of the present study showed that hairdressers are chronically exposed to high concentrations of formaldehyde in the work environment and these exposures are predominantly associated with work processes and ventilation of the workspace in which the hair straightening process is carried out. The results also showed that hair washing to remove excess product prior to the blow-drying and flat ironing stages considerably reduces the emanation and aspiration of formaldehyde vapors in the workplace, with consequent reduced exposure of the hairdressers to this chemical agent.

It can be concluded that the work process determines the levels of professional exposure, given that many variables of this process influence exposure intensity, i.e. the number of procedures performed during the day and/or per hour, density of professionals in the same salon performing the hair straightening procedure concurrently, and the length of procedure application time, where most hairdressers earn according to output.

The results for the other variables analyzed, such as physical structure of the salon, size of the work space, and use of ventilation, revealed that the greater the quantity of doors and windows, the lower the level of chemical exposure. The use of natural ventilation by opening of doors and windows and the use of ventilation systems can also help reduce exposure levels.

The social vulnerability of the addresses where the salons are located also had no significant impact on the exposure of the hairdressers, although higher concentrations of formaldehyde were detected in smoothing products at salons with IPVS 3 (city center with down-market businesses), in which the cost of the procedure was lower compared to salons located in regions of higher social vulnerability.

The initial hypothesis was that formaldehyde levels are higher in products used in regions of greater social vulnerability, a theory disproven by our results. This finding might be explained by the fact that down-market salons were located in geographic regions with different social vulnerability indices.

The present study also showed that none of the products used for hair straightening complied with the law, with formulas containing high levels of formaldehyde; i.e., analysis of the smoothing products commercially available revealed that their compositions differed to those stated on labels.

Although the analysis of the straightening products showed a high formaldehyde concentration in their formulations, levels well above ANVISA’s limits, these levels were not directly proportional to the degree of exposure of the professionals to formaldehyde.

The health issues reported by the professionals interviewed included ergonomic problems, such upper and lower limb pain, and also symptoms related to respiratory problems, reported by the majority of the hairdressers interviewed.

Recommendations

The beauty and cosmetic segment continues to face structural shortcomings and other challenges. Although technical standards have advanced and professionalization increased, many issues still need addressing to improve the working environment.

In view of the results reported, the awareness of hairdressers should be raised regarding effective measures for exposure prevention and control, through the use of ventilation in the work space where the straightening procedure is performed and guidance on the practice of washing the client’s hair prior to the blow-drying and flat ironing stages to promote more effective reduction of formaldehyde concentrations in the work environment.

The results found should be disseminated to raise hairdressers’ awareness of the risks inherent to the work carried out and to promote the adoption of preventive measures and standardization of work processes to reduce the risks of exposure to toxic substances harmful to health. Preventive measures to attenuate ergonomic risks are also key to enhancing the quality of life of these professionals.

Stricter inspection and control of products used for smoothing is also warranted, given that none of the package labels warned they contained formaldehyde level above those permitted by law. Therefore, more rigorous control by authorities is recommended, such as making the use of general dilution and exhaust ventilation systems compulsory, as well as evaluation and structural inspection of salons before issuance of an operation license.

Finally, another important factor to promote awareness and control of some types of work-related diseases is employee involvement in the planning of surveillance actions, notification of workers exposed to toxic substances in the workplace and systematic control of these substances, promoting joint responsibility of government and society for controlling a host of diseases, including work-related cancer, toward the prevention of hazards to worker and public health.

Considering the fact that formaldehyde is a highly toxic chemical agent with carcinogenic potential, the ideal would be that this substance would be totally abolished in the manufacture of cosmetics, since studies indicate the occupational exposure to formaldehyde and its relation with nuclear alterations, DNA damage, and, consequently, increased risk of mutations (Ladeira 2009). Therefore, it is worth mentioning that the aforementioned recommendations can minimize exposure but not eliminate it altogether.