1.1.2.2 Allergic contact dermatitis

Allergic contact eczema, contact dermatitis.

 An estimated 15–20% of the general population suffers from contact allergy

Allergic contact dermatitis is a common type of dermatitis caused by delayed hypersensitivity reaction (type IV) to exogenous (contact-) allergens (haptens) in contact with the skin.

Allergic contact dermatitis is mediated by allergen-specific sensitized T cells and is a form of type IV reaction, according to Gell and Coombs. Immunological sensitization time is at least 5-10 days; clinical symptoms may first develop after months to years. The dermatitis appears in sensitised individuals after a latency period of 8-24 hours, occasionally longer. Individual allergens have varying degrees of allergic potential. Most frequent contact allergens are metals, rubber ingredients, preservatives and occupational substances.

The reaction starts at the site of allergen exposure as an acute papulo-vesicular eruption which soon becomes eroded and forms an exudate. It is accompanied by intense pruritus. The lesions present with irregular border, spreading outside area of contact. Later, scaling and crusting can occur. In chronic forms, lichenification and fissuring dominate. Sometimes, allergic contact dermatitis may present as a chronic disease without an acute clinical phase.

The localisation depends on the type of exposure. Extensive (haematogenous) contact dermatitis may by caused by systemic exposure (ingestion, inhalation) of contact allergens. The affected site is a clue to the possible culprit allergen. Face: cosmetics, airborne allergens (paint vapours or pollens). Ears: jewellery, glasses, hearing aids. Lips: cosmetics, herpes simplex medications. Forehead/neck: shampoos, hair dyes. Neck/fingers/wrist: jewellery. Hands: occupational and recreational contact allergens. Axillae: deodorants. Feet: shoes, antifungals. Mouth: dentures, other dental products. Lower leg: elastic stockings, medications for leg ulcers.

The allergen causing contact dermatitis may be determined by patch testing. Several series of patch tests can be used: standard series of most frequent allergens, special series for peculiar occupational diseases, own substances brought by the patient. ROAT (repeated open application test) may be useful for low allergenic substances.

Cutaneous histology of the lesions shows parakeratosis, spongiosis, acanthosis, and an inflammatory lymphohistiocytic infiltrate with exocytosis of lymphocytes into epidermis.

The clinical features usually subside after 1-2 weeks of allergen avoidance; contact sensitivity usually persists indefinitely.

Allergic contact dermatitis can be complicated by impetiginization, the disease can become chronic (even after allergen avoidance). The lesions can disseminate and cause erythroderma. 

It is mandatory to seek the causative allergen by performing detective work (detailed history - work, hobbies, habits), and patch testing oriented by the history.

Allergic contact dermatitis must be differentiated from other inflammatory diseases such as psoriasis and dermatophyte infection in case of foot and hand involvement. It must also be differentiated from therapy-resistant localized dermatitis: Bowen’s disease, Paget’s disease of the nippleand lupus vulgaris. Reaction to latex can cause an IgE-mediated immediate type allergy in addition to a type IV allergic reaction to rubber accelerators.

It is very important to avoid contact with the causative allergens, and also with concomitant irritants (e.g. by using soap substitutes). Topical therapy consists of wet dressings or baths, and mainly corticosteroids in the appropriate vehicle (ointment, cream, lotion) chosen according to the nature of skin lesions. Phototherapy may be indicated in some cases. Alitretinoin (retinoid) can be used in severe refractory hand dermatitis.