The simple definition of dermatitis is inflammation of the skin. Many people think of dermatitis as synonymous with eczema but this is actually not true. Almost any rash can be thought of as a dermatitis based on this definition - including psoriasis, skin cancer, and seborrhea. However, we don't call every rash a dermatitis.
The rash of dermatitis is itchy, red, and may or may not have distinct margins. The specific look of the rash depends on the amount of time it has been present. Acute dermatitis has blisters, subacute dermatitis has scaling and crusting, and chronic dermatitis has lichenification.
There are several distinct types of dermatitis that are delineated by the causative agent or the cellular mechanism responsible for the rash.
Atopic dermatitis is sometimes called eczema or atopic eczema. But atopic dermatitis is only one of many types of eczema.
See also: *Lymphedema