Merck Manual

Please confirm that you are a health care professional

honeypot link

Definition of Dermatitis



Thomas M. Ruenger

, MD, PhD, Georg-August University of Göttingen, Germany

Last full review/revision Feb 2021| Content last modified Feb 2021
Click here for Patient Education

The meaning of the word "dermatitis" is inflammation of the skin. However, in clinical dermatology, dermatitis is used to describe a variety of different skin conditions that share the same inflammatory reaction pattern with similar clinical manifestations.

Histologically, lymphocytes extravasate into the dermis and then migrate into the epidermis, triggering intercellular epidermal edema (spongiosis), hyperproliferation, thickening, and hyperkeratosis. The dermatopathologic term for this process is spongiotic dermatitis or eczematous dermatitis. Although different types of dermatitis may differ in some minor histologic features, they cannot be clearly differentiated by histologic features alone.

Eczema is synonymous with dermatitis but is often used, mainly by non–health care practitioners, to mean atopic dermatitis (a specific type of dermatitis). Lichenoid dermatitis and interphase dermatitis are histologic terms and do not indicate dermatitis clinically.

The term "exfoliative dermatitis" should no longer be used. It was previously used to describe erythroderma. Erythroderma can be caused by a dermatitis, but it can also be caused by nondermatitis skin disorders.

Symptoms and signs of dermatitis disorders result from their histologic features:

  • Erythema (due to dermal inflammation and increased blood flow)

  • Skin thickening (due to cellular epidermal infiltrate and edema)

  • Scaling (due to hyperproliferation of the epidermis and hyperkeratosis)

  • Pruritus (possibly due to histamine released during inflammation)

  • Erosions and possibly oozing, crusting, and secondary infection, all resulting from pruritus-induced scratching

The most prominent manifestations in the acute phase of dermatitis are erythema and scaling. The most prominent manifestations in the chronic phase of dermatitis are skin thickening and lichenification.

Click here for Patient Education
NOTE: This is the Professional Version. CONSUMERS: Click here for the Consumer Version
Professionals also read

Test your knowledge

Pressure Injury
Pressure ulcers (PUs) are defined as areas of necrosis and ulceration where tissues are compressed between bone and hard surfaces, such as a bed or chair. There are many risk factors for PUs, which include age > 65 years, decreased mobility, and impaired sensation, among others. Of the main factors that influence the development of PUs, which of the following contributes to PUs but is not a direct cause?  
Download the Manuals App iOS ANDROID
Download the Manuals App iOS ANDROID
Download the Manuals App iOS ANDROID

Also of Interest