Effects of Capsaicin and Topical Anesthesia on Nonimmunologic Immediate Contact Reactions to Benzoic Acid and Methyl Nicotinate

Summary

The effects of topical capsaicin (a liberator of substance P) and topical anesthesia were studied in order to obtain information about the role of sensory nerves and substance P in the pathophysiology of nonimmunologic immediate contact reactions (NIICRs) induced by benzoic acid (BA) and methyl nicotinate (MN) in human skin. BA 500, 250, 125, 62, and 31 mM and MN 50, 25, 13, 7, 3, 1.5, and 0.75 mM in petrolatum were tested on the skin areas pretreated with capsaicin solution in 13 test subjects. BA 500, 125, 62, and 31 mM and MN 25, 10, 2, and 0.5 mM in petrolatum were tested on skin areas of 15 test subjects, anesthesized with a topical anesthetic cream (lidocaine 25 mg/g, prilocaine 25 mg/g). Prick tests with histamine dihydrochloride (10 mg/ml) were also performed on test and reference areas. Reactions were monitored 40 min after application with laser-Doppler flowmetry, and the sizes of erythema and edema reactions were measured. Capsaicin treatment inhibited erythema reactions to histamine, but did not inhibit erythema or edema from BA and MN. Topical anesthesia inhibited erythema and edema reactions to histamine as well as to BA and MN. These results suggest that neither erythema nor edema reactions to BA and MN are mediated by mechanisms sensitive to capsaicin (substance P). The mechanism by which a topical anesthetic inhibits skin reactions may result from its effect on cutaneous nerves, or it may have general antiinflammatory properties.