As Americans, we seem to have at least one favorite sports activity-jogging, cycling, tennis, swimming, skiing, backpacking, mountain climbing-you name it. With so many active people, it’s not surprising that there are frequent injuries and illnesses related to sports. Though exercise increases health, certain hazards go along with it. These include the increased possibility of direct injury to your skin. You expose yourself to many contagious skin diseases in the locker room, on the gym mats and from direct contact with infected people. The sweating, friction and stress you may put yourself through can create the ideal environment for new skin conditions to develop or for existing ones to get worse.

From acne to sun poisoning to herpes to "jogger’s nipples" to "turf toe" or "bikini bottom," the competitive and weekend athlete alike risk a line up of skin problems. Let’s look at some of these sports-related skin troubles.

Boxing, wrestling and other close contact sports.

Anytime you have close contact with another person you expose yourself to possible bacterial and viral infections. One common hazard of close contact sports is impetigo, a highly contagious bacterial infection you can get from infected opponents as well as from dirty gym mats. Impetigo gets a foothold on damaged skin, a common result of the friction and scraping from wrestling and other contact sports.

Boils are bacterial infections of the hair follicle. These painful, shiny, bright-red swellings of the skin usually develop over the elbows, forearms and knees after a bruise or a break in the skin. You should see a physician if you think you have boils.

Herpes simplex infections and dimple warts are viral infections associated with contact sports. Herpes simplex infections are so common in wrestlers that they’re sometimes called "herpes gladiatorum." The highly contagious dimple warts (molluscum contagiosom) also plague wrestlers, spreading easily in the warm, moist areas caused by heavy sweat.

If infections aren’t enough, close contact sports also increase the risk of scabies, a very contagious and terribly itchy infestation. Scabies mites can live on dirty mats and on the bodies of your opponents. Close contact sports can encourage a variety of other attacks on your skin including cuts, bruises, lacerations, abrasions and mat burns.

Some team sports create special problems because of the combination of rough activity and tight-fitting and bulky padding and uniforms.

Acne mechanic, an infection of the hair follicles where the concentration of the oil glands is high results from the rubbing, pressure, heat and swelling caused by bulky sports equipment, football helmets, catcher’s masks, and heavy, protective padding. This infection can also be picked up by performing bench presses. Boils are another common problem of team players because of the frequent skin injuries and the warm, moist conditions these infections love to grow in.

Turf toe, which appears as a red, swollen and painful big toe, is a unique skin problem caused by playing on artificial turf. Turf burns are abrasions that scrape off part of the skin, usually over the elbows, forearms and knees.

Long distance swimmers often suffer from a bacterial infection called swimmer's ear. Exposure to water for a long time dissolves the normal oils in their canals, softening and weakening the tissues. Unfriendly bacteria can multiply and cause itching, swelling, pain, tenderness and yellowish discharge from the ear. Dimple warts are also a common problem in swimmers.

Bikini bottom is a mild infection of the skin that results from wearing a wet bathing suit. This annoying infection frequently shows up when the sweat pores become clogged, trapping the bacteria that usually live on the skin in friendly and harmless numbers. Unable to escape, the trapped germs begin to proliferate, spread and cause trouble.

A common problem for runners and joggers are plantar warts, or warts on the soles of the feet. The warm, moist condition of running shoes encourage the growth of the virus that causes these warts. Corns are another problem of joggers. These are often caused by improperly fitting shoes, especially those that are too narrow.

Jogger’s toe, also known as tennis toe, is another complaint of joggers, runners, tennis players and mountain climbers. Appearing as a bruise beneath the toenails, usually on the big toes, this harmless discoloration is caused by ill-fitting shoes and sudden stops which force the toes into the front of the shoe, bending the nails and breaking the blood vessels. Soft, comfortable shoes with plenty of room as well as trimming the toenail straight across, can prevent this problem of "short stops."

Jogger’s nipple is an uncomfortable problem that can affect both sexes. It is an injury caused by friction in women who run without wearing bras and in men who jog in cotton T-shirts. The nipples become sore and red and may even bleed. To prevent this annoying condition, coat your nipples with Vaseline and wear a bra or a shirt with smooth, hard finish, such as those made of silk or semi-synthetic fabrics.

Gymnasts, dancers and others who do heavy stretching activity commonly develop stretch marks. These are thin scars that show up when the skin is distended or stretched over a long period of time. They are not a sign of disease. Gymnasts may also suffer from warts on their palms and fingers. This common viral infection can spread from contact with gym mats, parallel bars and other gymnastics equipment.

Direct exposure to the sun or rays reflected off snow, sand and water can create skin problems for both summer and winter athletes. Sunburn and sun poisoning are common in baseball and tennis players, golfers, mountain climbers, swimmers and skiers. For skiers and mountain climbers, it’s important to remember that the effect of ultraviolet light are stronger at higher altitudes.

Winter sports carry the added risk of frostbite from exposure to extreme cold. Wearing several layers of this clothing, rather than one or two heavier layers can help prevent frostbite. Also, because natural skin oil offers some protection to the skin, wait to shave and wash your face until after you’ve come in from the cold.

Skiers frequently suffer from dry, chapped skin caused by winter’s low temperatures and low relative humidity.

Heavy sweating, heat and fitted clothing go along with many sports activities and play a part in softening and weakening the upper layers of the skin that normally protect us against the invasion of harmful microorganisms-bacteria, viruses, fungi, and the scabies mite.

Athlete’s foot is the infection most clearly associated with sports. Caused by a fungus, this mildly contagious disorder spreads where there is heavy sweating and poor foot hygiene. It is a frequent visitor in the locker rooms, shower stalls and other warm, moist surroundings where bare feet tread.

Jock itch is a common infection of the groin caused by a fungus or yeast. Like athlete’s foot, it is related to sweating and warm, moist environments.

Allergic rashes are troublesome to all types of athletes and can be caused by many natural or manufactured products such as plants (poison ivy), clothing (shoes, gloves) and sports equipment (leather grips of raquets and golf clubs, basketballs, bar bells, wet suits and rubber diving masks, fiberglass in hockey sticks, gym mats, adhesive tape, etc.) Sweating always makes these allergic rashes worse.

Heat perspiration, friction, sun exposure and the emotional stress of competitive sports can cause or aggravate many skin problems.

Acne, for example, is worsened by the pressure and friction of the facemasks, helmets and the bulky padding of football uniforms. Eczema flares up with heat, perspiration and emotional stress. Hives can be provoked by heavy exercise, quick changes in body temperature and stress.

In addition, athletic activities expose you to a whole batch of skin injuries. Wearing new or poorly-fitting shoes, subjecting your feet to friction and pressure they are not used to can quickly lead to friction blisters on your feet and toes. These can be treated by letting your feet rest, keeping them dry, wearing two pairs of socks (each of a different fabric) and using foot powder.

Slamming your feet down can cause a pinching type of injury called "black heel’’. As its name says, this condition appears as a black patch over the

heel caused by a small hemorrhages or bleeding in the upper layers of the skin, often causing concern that it might be a malignancy. It occurs almost exclusively in teenagers who play hard surface sports (basketball, tennis, handball and squash) and it disappears without treatment.

Callus formation, particularly on the feet, is the most common mechanical injury in athletes. Calluses, and their close cousins corns, are the skin’s natural reaction to repeated rubbing and friction. These firm, thickened patches develop at points of pressure, especially over bony spots such as your heels. Gymnasts, oarsmen, golfers and tennis players often develop them on their hands. You can treat calluses by reducing the friction or pressure with pads, wraps or orthopedic appliances. Ingrown toenails can also occur and are often found on the big toes of many athletes. This results from poorly fitting or tight shoes and poor hygiene.

Even though athletes can always expect injuries, including those to the skin, there is no reason to be fearful about participating in competitive or recreational sports. You can prevent trouble by practicing good, wearing clothing and sports equipment that fit properly and protecting yourself from the sun, intense cold and insects. Remember that the best offense is a good defense. Protect yourself and your skin.

(Dr. Jerome Litt is an Assistant Clinical Professor of Dermatology at Case Western Reserve University School of Medicine and is in private practice in Beachwood. He is also a member of The Academy of Medicine of Cleveland/The northern Ohio Medical Association.)