Healthy skin provides a barrier between the inside of the body and the outside environment. A rash means some change has affected the skin.

Rashes are generally caused by skin irritation, which can have many causes. A rash is generally a minor problem that may go away with home treatment. In some cases a rash does not go away or the skin may become so irritated that medical care is needed.

In adults and older children, rashes are often caused by contact with a substance that irritates the skin (contact dermatitis). The rash usually starts within 48 hours after contact with the irritating substance. Contact dermatitis may cause mild redness of the skin or a rash of small red bumps. A more severe reaction may cause swelling, redness, and larger blisters. The location of the rash may give you a clue about the cause.

Contact dermatitis does not always occur the first time you are in contact to the irritating substance (allergen). After you have had a reaction to the substance, a rash can occur in response to even very small amounts of the substance. Contact dermatitis is not serious, but it is often very itchy. Common causes of contact dermatitis include:

• Poisonous plants, such as poison ivy, oak, or sumac.
• Soaps, detergents, shampoos, perfumes, cosmetics, or lotions.
• Jewelry or fabrics.
• New tools, toys, appliances, or other objects.
• Latex. Allergy to natural rubber latex affects people who are exposed to rubber products on a regular basis, especially health care workers, rubber industry workers, and people who have had multiple surgeries. Latex allergies can cause a severe reaction.

Rashes may occur with viral infections, such as herpes zoster; fungal infections, such as a yeast infection (Candida albicans); bacterial infections, such as impetigo; and sexually transmitted diseases (STDs). Rashes may also occur as a symptom of a more serious disease, such as liver disease, kidney disease, or some types of cancer.

Rashes may also appear after exposure to an insect or a parasite, such as the scabies mite. You may develop a rash when you travel to a rural area or go hiking or camping in the woods.

A rash may be a sign of a chronic skin problem, such as acne, eczema, psoriasis, or seborrheic dermatitis. Other causes of rash include dry, cold weather; extremely hot weather (heat rash); and emotional stress. Emotions such as frustration or embarrassment may lead to an itchy rash.

The need for medical treatment often depends on what other symptoms are present. A rash that occurs with other symptoms, such as shortness of breath or fever, may mean another problem, such as a serious allergic reaction or infection.

A very rare and serious type of generalized red rash is toxic epidermal necrolysis (TEN). This rash may cause the skin to peel away, leaving large areas of tissue that weep or ooze fluid like a severe burn. If this type of rash occurs, you need to see a doctor. TEN may occur after the use of some medicines.

Review the Emergencies and Check Your Symptoms sections to determine if and when you need to see a doctor.