Dermatitis is an inflammation of the skin. It can have many causes and occurs in many forms. It usually involves an itchy rash on swollen, reddened skin.

Skin affected by dermatitis may blister, ooze, develop a crust or flake off. Examples of dermatitis include atopic dermatitis (eczema), dandruff and rashes caused by contact with any of a number of substances, such as poison ivy, soaps and jewelry with nickel in it.

Dermatitis is a common and not contagious, but it can make you feel uncomfortable and self-conscious.

A number of health conditions, allergies, genetic factors and irritants can cause different types of dermatitis:

Atopic dermatitis (eczema) is likely related to a mix of factors, including dry skin, a gene variation, an immune system dysfunction, bacteria on the skin and environmental conditions.

Contact dermatitis results from direct contact with one of many irritants or allergens — such as poison ivy, jewelry containing nickel, cleaning products, perfumes, cosmetics, and preservatives in many creams and lotions.

Seborrheic dermatitis may be caused by a yeast (fungus) that is in the oil secretion on the skin. People with seborrheic dermatitis may notice their condition tends to come and go depending on the season.

Numerous risk factors can increase development of certain types of dermatitis:

Age. Dermatitis can occur at any age, but atopic dermatitis (eczema) usually begins in infancy.

Allergies and asthma. People who have a personal or family history of eczema, allergies, hay fever or asthma are more likely to develop atopic dermatitis.

Occupation. Jobs that put you in contact with certain metals, solvents or cleaning supplies increase your risk of contact dermatitis. Being a health care worker is linked to hand eczema.

Health conditions. You may be at increased risk of seborrheic dermatitis if you have one of a number of conditions, such as congestive heart failure, Parkinson's disease and HIV.

Source: Mayo Clinic www.mayoclinic.org