Slide show: Common skin rashes

Your skin is surprisingly resistant to a wide variety of assaults, but it's still susceptible to various invaders. Viruses, parasites, fungi, heat and medications can all cause skin rashes and eruptions.

Though not life-threatening, rashes are often bothersome, uncomfortable or even painful. Some, such as heat rash and swimmer's itch, clear up on their own. Others, including rosacea and drug rashes, require medical treatment. Here's a look at common skin rashes, their causes and when you might need to see your doctor.

This form of dermatitis, commonly referred to as eczema, is a chronic condition that causes itchy, inflamed skin. Most often, it occurs in the folds of the elbows, backs of the knees or the front of the neck. It tends to flare periodically and then subside for a time, even up to several years. The exact cause of this skin disorder is unknown, but it may result from a malfunction in the body's immune system.

Even mild cases of atopic dermatitis can be extremely itchy. Self-care measures, such as avoiding soaps or other irritants and applying creams or ointments help. See your doctor if your symptoms distract you from your daily routines or prevent you from sleeping.

Named for its sweeping presentation, the Christmas tree rash is a fine, scaly rash that ranges in color from pink to tan. It often starts as one larger spot at the spine or the midline of the back or front of the body (herald patch) and spreads outward. The rash, which may be caused by a virus, is usually only mildly itchy and may flake or peel.

This skin condition is common in teenagers and young adults and occurs more frequently in the fall and spring. It usually resolves without treatment in four to six weeks but can last up to 12 weeks. Contact your doctor if the rash is uncomfortable or painful.

Contact with an irritant or allergen causes this form of dermatitis. Irritant contact dermatitis (A) produces red, dry itchy patches usually on the hands, fingers and face. Common irritants include soap, detergents and skin-cleaning products. Allergic contact dermatitis (B) produces a red rash, bumps and sometimes blisters. Common allergens include rubber, metals such as nickel, costume jewelry, perfume, cosmetics, hair dyes and weeds such as poison ivy.

If you can identify and avoid the offending agent, the inflammation resolves without treatment in two to three weeks. See your doctor if your symptoms continue beyond that time frame or if the rash is uncomfortable or painful.

Any medication can produce a drug rash — an allergic reaction to a medication. But the most common culprits include antibiotics, anti-seizure medications and diuretics. The rash usually starts within two weeks of taking a new medication and begins as discrete red spots that spread, covering large areas of the body.

A drug rash could be a part of a more serious and potentially life-threatening allergic reaction. Contact your doctor promptly if you experience a rash after taking a medication. He or she can determine a treatment option that likely includes an alternative medication. A drug rash usually resolves one to three weeks after discontinuing the medication.

Miliaria rubra (A), one type of heat rash, appears as red clusters of small blister-like bumps that can produce a stinging-like sensation. Miliaria crystallina (B), on the other hand, appears as clear, fluid-filled bumps that produce no other signs or symptoms. Caused by active sweat glands, heat rash usually develops on the neck, upper chest, groin, under the breasts and in elbow creases.

This rash isn't serious. It often resolves with proper self-care methods, such as keeping the affected areas cool and dry, avoiding tight, restrictive clothes, and not using heavy ointments or creams when you expect heavy perspiration.

In most cases, intertrigo occurs in warm, moist areas where skin rubs or presses together, such as under the arms, in the groin area, between abdominal folds or under the breasts (as seen in the image). Moisture, bacteria or fungi can cause intertrigo, which is usually red and painful. In severe cases, the skin may crack and bleed.

This condition often resolves with proper self-care methods, such as keeping the affected areas dry and avoiding tight, restrictive clothes. See your doctor if the inflammation moves beyond the skin fold or if the affected area is painful.

Typically, this rash appears as rows of itchy, flat-topped bumps (lesions) on the arms and legs. It can also involve the scalp or the mucous membranes that line the mouth, nose, vagina and anus. In some cases, lichen planus results from an allergic reaction to a medication or from chronic hepatitis. But in most cases, doctors are unable to identify a cause.

Lichen planus occurs most often in middle-age and isn't usually serious. The rash can last months or even years and may reappear after it goes away. When present in the mouth, it's important to see your doctor to reduce your symptoms and to speed the healing of the lesions. Though rare, long-term lichen planus in the mouth can result in the development of skin cancer.

With psoriasis, the life cycle of skin cells speeds up, resulting in a rapid buildup of rough, dead skin cells. These skin cells accumulate, forming thick silvery scales and itchy, dry, red patches that are sometimes painful. The inflammation — which usually affects the knees, elbows, trunk and scalp — tends to flare periodically and then subside for a time. Psoriasis almost always returns, however. Psoriasis may occur in combination with arthritis.

For some people, this chronic condition is a mild nuisance. For others, it's totally disabling. Talk to your doctor if your skin condition moves beyond the nuisance stage and causes you discomfort and pain, if it makes performing routine tasks difficult, or if you're concerned about the appearance of your skin.

Despite its name, ringworm isn't caused by a worm but rather a fungus. It appears as itchy, red, scaly, slightly raised, expanding rings on the trunk of the body, face, groin or thigh fold. The ring grows outward as the infection spreads, and the center area becomes less actively infected. Ringworm is contagious and spreads several ways, including from skin-to-skin contact or contact with a contaminated object such as unwashed clothing. It can also spread from animal to person.

This infection may resolve without treatment within four weeks, but it usually requires a prescription medication to clear up. If you experience swelling, drainage, fever or excessive redness, see your doctor immediately.

Though rosacea can look like acne, it's actually a chronic, inflammatory skin condition of adults. It causes redness in the face and produces small, red, pus-filled bumps or pustules. Rosacea mainly affects those between the ages of 30 and 60, especially people with lightly pigmented skin. The cause of rosacea is unknown, but researchers believe it's likely due to a combination of genetic and environmental factors.

For most people, rosacea is cyclic, meaning it tends to flare up periodically, lessen in intensity, and then flare up again. Though it doesn't have a cure, treatments can control and reduce the symptoms. If you experience persistent redness of your face, see your doctor for a diagnosis and proper treatment.

Herpes zoster, more commonly known as shingles, develops when the virus that causes chicken pox (varicella zoster) reactivates after lying dormant within the nerve cells. As this virus reactivates, pain or tingling starts in a limited area, usually only on one side of the body or face. Subsequently, a rash with small blisters appears. These blisters break, leaving behind superficial ulcers that dry and form crusts.

Shingles usually resolves in two to three weeks without treatment. Contact your doctor if your symptoms continue beyond that time frame or if the condition remains uncomfortable or painful. Also, if a rash develops anywhere near your eyes, see your doctor immediately. If left untreated, shingles in this area could lead to temporary or permanent blindness.

Parasites in contaminated water can enter the superficial layers of exposed skin — skin not covered by a swimsuit, wet suit or waders. The organisms soon die and cause a skin reaction called swimmer's itch. Initially, the reaction is mild and consists of redness of the affected skin followed by itchy, red, raised areas. On subsequent exposures to the organisms, the reaction can be more severe and persistent, sometimes causing blisters.

Swimmer's itch isn't serious and usually resolves without medical treatment within one week. See your doctor if the rash doesn't clear up in this time frame or if you're uncomfortable or in pain.