Athletic activity may cause or aggravate skin disorders, which in turn may diminish athletic performance. Since many sporting activities necessitate prolonged exposure to the sun, athletes must avoid painful sunburn which will adversely affect their performance. Drugs and chemicals also may cause photoallergic and/or phototoxic reactions, including polymorphous light eruption and athletes should thus avoid photosensitising drugs and chemicals. The effects of chronic ultraviolet exposure include ageing, pigmentation and skin cancers. The most effective protection against excessive exposure to sunlight is the use of sunscreens, although inadequate application and poor protection in the UVA spectrum may diminish their effectiveness and contact allergies may create other problems. Viral, bacterial and fungal infections are common in athletes due to heat, friction and contact with others. Herpes simplex may be treated with any drying agents (e.g. alcohol) as they are as effective as more expensive topical agents such as acyclovir. Molluscum contagiosum may be spread by close contact or water contact and is treated by superficial incision, cryotherapy or standard wart varnishes. Plantar wart infection is transmitted by swimming pool decks, changing rooms and hand-to-hand from weights in gymnasiums. Plantar warts presenting with pain may be aggressively treated, by blunt dissection, but painless ones are best treated conservatively. Impetigo and folliculitis often develop after trauma. Antibiotics are effective against mild infections while abrasions and lacerations should be cleansed and dressed with occlusive dressings. Diphtheroid bacteria in moist footwear may produce pitted keratolysis and erythrasma. Tinea pedis is common in athletes and probably originates in swimming pools, gymnasium floors and locker rooms. Interdigital, dry-moccasin and pustular-midsole forms can be distinguished. The latter two forms respond to topical antifungal agents, while the interdigital form, a mixed fungal/bacterial infection, is treated with debridement, antibiotics and drying routine similar to the therapy of otitis externa. Nail infections by a variety of organisms may appear as onycholysis with or without paronychia and should be treated with the appropriate antibiotics. Tinea versicolor occurs in heat and humidity. Since Pityrosporum orbiculare is part of the normal flora it often recurs, necessitating regular treatment. Acute trauma injuries include contusions, black heel or petichiae of the heel, black toe (bleeding under the nail), 'jogger's nipple' caused by chafing, and foot blisters. Chronic trauma may result in calluses, corns and paronychia. Plantar corns can be disabling and may be caused by overly tight shoes or abnormalities in biomechanics; treatment includes restoring normal foot function and minimal surgical procedures. Paronychia is treated best by wedge resection.(ABSTRACT TRUNCATED AT 400 WORDS)