logo Dermatitis

Itchy skin disease



  • Be able to describe acute and chronic dermatitis.
  • Recognise distinguishing features for common forms of dermatitis.

Key points

  • The terms “dermatitis” and “eczema” are often used interchangeably.
  • Acute dermatitis is characterised by erythema, vesiculation and oozing.
  • Chronic dermatitis is characterised by lichenification (thick dry patches).
  • Most types of dermatitis are intensely itchy.
  • Management of dermatitis involves emollients, topical steroids and sometimes antibiotics.
  • Atopic dermatitis is characterised by onset in childhood, association with asthma and allergic rhinitis, dry skin and intermittent flare-ups.
  • Atopic dermatitis is associated with IgE hypersensitivity and TH1 inflammatory cytokines.
  • Although commonly predominantly flexural, any site may be affected by atopic dermatitis.
  • Nummular (discoid) dermatitis is characterised by clusters of round or oval plaques.
  • Irritant contact dermatitis occurs at the site of cutaneous injury.
  • Irritants include friction, water, detergents, solvents and many other substances.
  • Allergic contact dermatitis is due to delayed hypersensitivity.
  • Allergic contact dermatitis is confirmed by epicutaneous patch tests.
  • Allergic contact dermatitis occurs at the site of cutaneous injury but often spreads.
  • Patch tests are removed after 48 hours and observed for a further 48 hours.
  • The most common contact allergens are nickel and fragrances.
  • Lichen simplex is a localised chronic dermatitis related to rubbing and scratching.
  • Pompholyx is a palmoplantar vesicular dermatitis.
  • Seborrhoeic dermatitis is a scaly dermatitis most often affecting sebaceous areas especially scalp and face.
  • Asteatotic dermatitis (eczema craquelé) is due to dry skin and usually affects the lower legs.
  • Venous eczema complicates venous insufficiency and is characterised by hyperpigmentation, and subcutaneous induration.
  • Autosensitisation refers to generalisation of an initially localised dermatitis.


Dermatitis and eczema are words that are often used interchangeably to describe a variety of distinct skin conditions in which there is epidermal and dermal inflammation and nearly always intense itching.

Acute dermatitis is characterised by erythema, vesiculation and oozing, often with oedema. Histologically, the hallmark of acute dermatitis is spongiosis (intraepidermal vesicles).

Histology of eczema


Dermal inflammatory infiltrate

Subacute dermatitis is similar but with scaling and crusting. Chronic dermatitis results in thickened dry patches, and is often lichenified from chronic rubbing (increased skin markings). Lichenification is often predominantly follicular in pigmented skin.

Types of dermatitis:

Atopic dermatitis

Read more about atopic dermatitis on DermNet.

Students are expected to have in depth knowledge about atopic dermatitis because it affects up to 20% of the population and causes considerable distress and ill health. Its prevalence is greatest in childhood, generally starting in the first few months of life, becoming more severe in infancy and often improving in school years.

Diagnosis depends on clinical findings, which vary with the age and stage of the disease. The main features are:

Flare-ups may be precipitated by:

Atopic eczema is frequently complicated by infection with Staphylococcus aureus and sometimes Streptococcus pyogenes (impetiginised eczema) and less frequently by Herpes simplex (eczema herpeticum). Warts and molluscum contagiosum tend to be more prevalent and extensive.

Impetiginised eczema

Molluscum contagiosum and atopic dermatitis

Eczema herpeticum

The pathogenesis appears involve release of vasoactive substances from mast cells and basophils as an IgE-mediated hypersensitivity reaction. There is a TH2 pattern of cytokine release from T helper lymphocytes in the epidermis and dermis with low levels of TH1 lymphocytes and gamma interferon. It is not known why the incidence of atopic dermatitis appears to be increasing; theories include increased hygiene and decreased exposure to micro-organisms and greater exposure to house dust mite. Prick tests are often positive but are not useful in making the diagnosis.

Affected sites vary with age. Infantile eczema commonly affects the face, sparing around the mouth and later the hands, feet and elsewhere. In older children, eczema tends to affect flexures, particularly antecubital and popliteal fossae. Adults frequently develop irritant hand eczema. Bilateral nipple eczema is common. Erythrodermic eczema refers to involvement of the entire body and the patient may require hospitalisation for wet dressings and sedation.

Infantile ezema

Subacute flexural eczema

Chronic lichenified eczema

Atopic hand dermatitis

Nipple eczema

Wet dressings for erythrodermic eczema

Management of atopic eczema involves:

Nummular or discoid dermatitis

Read more about nummular or discoid dermatitis on DermNet.

Nummular or discoid dermatitis/eczema has two forms, resulting in acute exudative plaques or less inflamed dry patches for weeks to months. It may arise at any age. Clusters of round or oval plaques may be localised to lower legs or other sites or generalised. The initial lesion may be precipitated by trauma or infection.

Dry discoid eczema

Infected discoid eczema

Close-up discoid eczema

Management of nummular dermatitis involves:

Irritant contact dermatitis

Read more about irritant contact dermatitis on DermNet.

Irritant contact dermatitis arises when the skin is exposed acutely or chronically to chemical or physical agents that damage the skin. Irritant hand dermatitis is very prevalent in certain occupations such as cleaning and hairdressing, especially in atopic subjects. Irritant reactions include:

Typical irritants include friction and abrasion, water, dry and/or cold air, detergents, solvents, acids and alkalis, oxidising and reducing agents, prickly plants and fibreglass, enzymes, dirt, urine (napkin dermatitis) and many other substances.

Irritant dermatitis occurs at the site of direct injury to the cells. Gradual onset of dermatitis arises from loss of the skin barrier and inadequate repair mechanisms. It can be confused with or coexist with allergic contact dermatitis.

Dermatitis caused by benzoyl peroxide acne cream

Dribble rash

Irritant hand dermatitis

Management of irritant contact dermatitis involves:

Allergic contact dermatitis

Read more about allergic contact dermatitis on DermNet.

Allergic contact dermatitis refers to cutaneous delayed hypersensitivity reactions and may be confirmed by patch testing. The dermatitis may be acute, subacute, chronic or relapsing and may coexist with another form of dermatitis.

The pattern of distribution may give a clue to the origin, but although it may initially be confined to sites of contact the dermatitis may spread or generalise. Very small amounts of the allergen may be sufficient to cause dermatitis in sensitised individuals.

Shoe dermatitis: rubber antioxidant allergy

Plant dermatitis: toxicodendron allergy

Adhesive plaster dermatitis: rosin (colophony) allergy

Some examples:

Management of allergic contact dermatitis is similar to irritant contact dermatitis.

Patch tests

Dermatologists use epicutaneous patch tests to identify contact allergens but interpretation of the results requires considerable experience. The standard series of about 24 common contact allergens may be supplemented by numerous other known or suspected compounds in low concentration. The test substances are applied to small plastic or aluminium chambers on special non-allergic tape. The patches are applied to the upper back and removed after 48 hours. The skin is observed over at least the next 48 hours. Eczematous reactions suggest contact allergy but may also be irritant in nature (non-allergic), especially in atopic subjects, and detected allergy may not be relevant to the presenting complaint.

The most common contact allergens include nickel, cobalt and chrome, fragrances, various anti-oxidant compounds used in the manufacture of rubber, preservatives and adhesives.

Patient presented with eyelid dermatitis of unknown cause

Patch tests applied to standard series, preservatives and fragrances

Positive patch test to ethylenediamine, present in a cream the patient was applying to itchy patches (Kenacomb)

Lichen simplex

Read more about lichen simplex on DermNet.

Lichen simplex chronicus is a localised form of dermatitis in which there is lichenification because of rubbing and scratching; the patches become increasingly itchy so it is difficult to stop scratching. Well-defined papules and bumpy thickened plaques are found most often in adults on the nape of the neck, occipital scalp, lower legs, forearms, vulva or scrotum.

Lichen simplex upper back

Lichen simplex of scrotum

Management of lichen simplex involves:

Nodular prurigo

Read more about nodular prurigo on DermNet.

Nodular prurigo is an uncommon chronic skin disease in which there are crops of intensely itchy firm nodules, sometimes associated with atopic dermatitis. Severe nodular prurigo is very debilitating and difficult to treat effectively. Individual lesions may be distinguished from squamous cell carcinoma by biopsy. Prurigo mitis or papular prurigo is a similar condition with itchy papules.

Widespread nodular prurigo

Close-up of excoriated nodular prurigo


Read more about pompholyx on DermNet.

Pompholyx, also known as dyshidrotic or vesicular palmar eczema, refers to acute, chronic or relapsing blistering of the fingers, palms and /or soles. Crops of irritable deep-seated vesicles are followed by scaling and fissuring of the affected areas and may be complicated by Staphylococcus aureus infection. Sweating in response to emotional stress or heat may precipitate vesicles in some individuals. Pompholyx sometimes presents as an id reaction to tinea pedis (‘one foot, two hands’ syndrome) or as an expression of contact dermatitis to nickel.

Severe bullous pompholyx

Dry phase of pompholyx

Management of pompholyx involves:

Seborrhoeic dermatitis

Read more about seborrhoeic dermatitis on DermNet.

Seborrhoeic dermatitis is a common chronic erythematous scaly dermatosis affecting the following sites:

Seborrhoeic dermatitis may affect infants, presenting within the first few months postpartum as cradle cap or napkin dermatitis and sometimes spreading widely. It is rare after the age of one year. Adult-type seborrhoeic dermatitis usually presents after the age of 20 but may occur any time after puberty.

Seborrhoeic dermatitis appears to be an inflammatory response to Malassezia yeasts, which proliferate in oily skin (seborrhoea). It sometimes progresses to psoriasis; unusually extensive seborrhoeic dermatitis is sometimes called “sebopsoriasis”. Seborrhoeic dermatitis is particularly troublesome in patients infected by human immunodeficiency virus and those with Parkinson’s disease.

Characteristically, the scale is yellowish and greasy or white and bran-like (pityriasiform) associated with variable nummular or annular pale pink to bright red patches. Itching tends to be absent or mild.

Facial seborrhoeic dermatitis

Axillary seborrhoeic dermatitis

Severe seborrhoeic dermatitis of scalp

Management of seborrhoeic dermatitis involves:

Asteatotic dermatitis

Read more about asteatotic dermatitis on DermNet.

Asteatotic dermatitis is also known as eczema craquelé and xerotic eczema and is due to the skin drying out. It generally affects the lower legs resulting in pruritic dry cracked red patches.

Asteatotic dermatitis

Management of asteatotic dermatitis involves:

Venous eczema

Read more about venous eczema on DermNet.

Venous eczema is also known as stasis or gravitational eczema and is a manifestation of chronic venous insufficiency following deep venous thrombosis. Varicose eczema is a variant associated with visible varicose veins. Venous eczema affects the lower legs. It may be unilateral or bilateral. There is a high risk of contact allergy so patch testing should be considered.

Features include:

Chronic venous eczema

Severe venous eczema with ulceration

Subacute venous eczema and atrophie blanche scarring

Varicose eczema

Management of venous eczema involves:

Autosensitisation dermatitis

Read more about autosensitisation dermatitis on DermNet.

Autosensitisation dermatitis is the rash that appears on the trunk and limbs due to generalisation of a previously localised condition such as asteatotic or venous eczema. It may appear similar to nummular dermatitis and can be intensely pruritic, requiring systemic steroids for control. An id reaction is autosensitisation dermatitis arising in response to a fungal infection.

Autosensitisation dermatitis

Severe autosensitisation dermatitis