Eczema that affects the scalp may sometimes be seborrheic dermatitis, which is a form of dandruff. According to The American Academy of Dermatology Association (AAD), scalp eczema tends to affect babies under the age of 3 months. In babies, scalp eczema is known as cradle cap. It usually clears up between the ages of 6 months and 1 year, but can return during puberty.