In some people, atopic dermatitis is related to a gene variation that affects the skin's ability to provide protection. With a weak barrier function, the skin is less able to retain moisture and protect against bacteria, irritants, allergens and environmental factors — such as tobacco smoke.
In other people, atopic dermatitis is caused by too much of the bacteria Staphylococcus aureus on the skin. This displaces helpful bacteria and disrupts the skin's barrier function.
A weak skin barrier function might also trigger an immune system response that causes the inflamed skin and other symptoms.
Atopic dermatitis (eczema) is one of several types of dermatitis. Other common types are contact dermatitis and seborrheic dermatitis (dandruff). Dermatitis isn't contagious.