The rash arises when the skin comes in contact with an allergen, a usually harmless substance that the immune system attacks. Allergens trigger allergic reactions. Allergens can come from certain soaps, creams and even pets. Your immune system might not react the first time you encounter an allergen.

Where do most rashes come from?

Skin rashes can occur from a variety of factors, including infections, heat, allergens, immune system disorders and medications. One of the most common skin disorders that causes a rash is atopic dermatitis (ay-TOP-ik dur-muh-TI-tis), also known as eczema.

How did I get a rash?

Rashes can be caused by many things, including exposure to certain plants (poison ivy, for example), allergic reactions to a medication or a food. Rashes can also be caused by an illness such as measles or chickenpox.