Health article

Rash Evaluation: MedlinePlus Medical Test

What is a rash evaluation?

A rash evaluation is a test to find out what is causing a rash. A rash, also known as dermatitis, is an area of skin that is red, irritated, and usually itchy. A skin rash may also be dry, scaly, and/or painful. Most rashes happen when your skin touches a substance that irritates it. This is known as contact dermatitis. There are two main types of contact dermatitis: allergic contact dermatitis and irritant contact dermatitis.

Allergic contact dermatitis happens when your body’s immune system treats a normally harmless substance as if it were a threat. When exposed to the substance, the immune system sends out chemicals in response. These chemicals affect your skin, causing you to develop a rash. Common causes of allergic contact dermatitis include:

  • Poison ivy and related plants, like poison sumac and poison oak. A poison ivy rash is one of the most common types of contact dermatitis.
  • Cosmetics
  • Fragrances
  • Jewelry metals, such as nickel.

Allergic contact dermatitis usually causes itching that can be severe.

Irritant contact dermatitis happens when a chemical substance damages an area of skin. This causes a skin rash to form. Common causes of irritant contact dermatitis include:

  • Household products such as detergents and drain cleaners
  • Strong soaps
  • Pesticides
  • Nail polish remover
  • Body fluids, such as urine and saliva. These rashes, which include diaper rash, most commonly affect babies.

Irritant contact dermatitis is usually more painful than itchy.

In addition to contact dermatitis, a rash may be caused by:

  • Skin disorders, such as eczema and psoriasis
  • Infections such as chicken pox, shingles, and measles
  • Insect bites
  • Heat. If you get overheated, your sweat glands can get blocked. This can cause a heat rash. Heat rashes often happen in hot, humid weather. While it can affect people of any age, heat rashes are most common in babies and young children.

Other names: patch test, skin biopsy

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