The exact cause of atopic dermatitis (eczema) is unknown. Healthy skin helps retain moisture and protects you from bacteria, irritants and allergens. Eczema is likely related to a mix of factors:1  Dry, irritable skin, which reduces the skin's ability to be an effective barrier.2  A gene variation that affects the skin's barrier function.ealthy skin helps retain moisture and protects you from bacteria, irritants and allergens. Eczema is likely related to a mix of factors: 1  Dry, irritable skin, which reduces the skin's ability to be an effective barrier. 2  A gene variation that affects the skin's barrier function.