Effects of Topical Menthol on Skin Blood Flow and Active Sweat Gland Density during Hyperthermia

Abstract

Topical application of menthol evokes cold sensation and cutaneous vasoconstriction without actual reduction in tissue temperature via the stimulation of a specific cold receptor family known as TRPM8. While being widely used to reduce joint pain, muscle inflammation, and soft tissue injuries in athletes and individuals with musculoskeletal disease, topical menthol may adversely affect body’s heat loss mechanisms. PURPOSE: To investigate if topical application of menthol reduces skin blood flow (SkBF) and active sweat gland density (ASGD) to the extent to which body heat loss is significantly reduced during recovery from exercise-induced hyperthermia. METHODS: Ten healthy male subjects (22±1 yrs) underwent two trials of cycle exercise at 50% VO2max in the heat (45°C, 50%) until their rectal temperatures (Tre) elevate 1.5°C above the baseline. Following the cessation of exercise, either 10g of 3.1% menthol gel (MEN) or placebo Lanolin cream (PBO) was applied on the limbs except hands and feet after which subjects recovered on a chair for 30min in thermoneutral condition (23°C, 50%). SkBF and ASGD were measured using a laser Doppler flowmetery and an iodine-impregnated cotton paper on ventral forearm and anterior thigh. Thermal measurements included Tre, 4-sites mean skin temperature (Tsk), and thermal sensation (TS: −4 very cold ~ 4 very hot). RESULTS: Cold TS in MEN was significantly greater than in PBO (F=29.22, P<.01) while reduction in SkBF and ASGD in MEN did not show significant difference compared to PBO. These slight alterations in vasomotor/sudomotor responses to topical menthol did not significantly impair Tre or Tsk recovery from hyperthermia.Table: No title available.CONCLUSION: Topical application of menthol does not adversely affect body heat loss during recovery from exercise-induced hyperthermia while significantly inducing cold TS.