Contact Dermatitis on the upper arm due to an allergy.

Every once and a while your skin may break out into a rash. You may or may not know what caused this to happen, and it could be a minor irritation or turn into something much worse. Doctors have a name for these topical rashes that can sometimes appear out of the blue, contact dermatitis.

According to, contact dermatitis is defined as "inflammation of the skin caused by an allergic reaction to contact with an animal, vegetable, or chemical substance." However, contact dermatitis can be caused by an allergy or by damage to the skin.

Contact dermatitis caused by an allergy

When your skin is exposed to a substance that it is allergic to, your immune system will respond to that substance. The rash is your body's immune system trying to fight off the allergen.  It typically takes being exposed to the substance multiple times before your body will react. The first time you are exposed to a potential allergen your body becomes sensitized, and it can take at least two additional experiences with the allergen before your body will react.

One example of this type of contact dermatitis is poison ivy rash. When a person who is sensitized to poison ivy comes in contact with the oily resin from the plant, called urushiol, the body reacts causing a painful, itchy rash. Some people are surprised to find themselves with a rash after they had thought they could not get poison ivy. In this case, it just took enough exposure to the plants before their body was sensitized to it and began to react.

With allergic contact dermatitis, the rash is usually found at the site where you came in contact with the substance you are allergic to.  It may take up to a few days for a rash to appear and it will typically itch and possibly burn. A more severe rash may blister or become a raised red rash.

Some typical causes of allergic contact dermatitis include:

  • Fragrances found in soaps, lotions, perfumes and other cosmetics
  • Hair dyes, perms or chemical straighteners
  • Poison ivy, poison oak or poison sumac
  • Nickel, commonly found in jewelry and belt buckles
  • Chemicals used in tanning leather
  • Latex rubber
  • Some topical medications
  • Citrus fruit, especially the peel

Contact dermatitis caused by skin damage

Sometimes your skin can break out into a rash even though it has not been exposed to an allergen. Your immune system is not reacting but a substance you have been in contact with has caused damage to your skin. This is referred to as irritant contact dermatitis and is more common with people who have eczema.

Irritant contact dermatitis usually appears immediately at the exposure site where something is in contact with your skin.  The rash can be more painful than itchy, and may also blister or become a raised red rash.

Talk to your doctor

It is always best to consult your doctor when you are not sure what caused your contact dermatitis. It is especially important to call a doctor when your rash is hot, red, severely burning, or very painful as it can be a possible sign of infection. Your doctor will advise whether an over-the-counter medicine or prescription is the best course of action to take.