Allergies Clinics of London

Our Allergies Centres .

Contact Dermatitis

What is Contact Dermatitis?

Contact dermatitis covers a range of delayed skin reactions that occur after direct skin contact with a sensitising agent or contact irritant.  This is common in adults in the workplace (Occupational dermatitis) and occurs in cleaners, caterers, mechanics, hairdressers, nurses and food handlers.  Triggers include hair products, jewellery, dyes in clothing, leather, rubber, glues, cement, raw food exposure, topical medications, sunscreens, cosmetics, fragrances and plants.  Irritant contact dermatitis accounts for over 80% of all contact dermatitis.  This occurs on the hands and other skin surfaces where chronic exposure to a cleaning agent or chemical induces a non-allergic localised skin irritation.  Allergic contact dermatitis involves a delayed T-cell mediated immune response which develops after exposure to a metal or chemical in the environment.  Contact Urticaria is a rapid onset localised urticaria seen in chefs and food handlers. 

Irritant Contact Dermatitis.

Irritant contact dermatitis is a common non-allergic condition which occurs on the hands of atopic people involved in the cleaning industry after frequent exposure and skin “insult” from detergents and water.  These agents remove the natural outer skin moisturisers and irritate the skin.  This cumulative and progressive skin dryness, scaling and fissuring leads to the typical exogenous dermatitis.  Solvents and cutting oils used in factories and workshops are triggers, as is ammonia residue in infantile nappy dermatitis.

Allergic Contact Dermatitis

Allergic Contact Dermatitis develops after repeated allergen exposure and is a T cell mediated delayed skin hypersensitivity to common metals, dyes, rubber products and cosmetics.  Common in non-atopic adult females (over 10% of females are Nickel allergic).  The lesions have sharply demarcated, occurring at the site of allergen exposure (or contact) and develop over 48 hours.  Initially there is redness and itching, followed by crusted vesicles and blisters, which becomes thickened skin with time.  These are limited to the site of exposure and resolve within weeks after allergen removal.  Many allergens causing contact dermatitis are chemicals (or haptens) that have to bind to a carrier protein to trigger a delayed immune response.  Certain specific areas of skin are primarily affected:  Nickel tends to affect the earlobes and fingers, hair dyes affect the scalp and face, leather shoe dyes affect the feet and nail varnish (santolite) or cosmetics affect the face and neck.  Minimal perspiration can elute contact allergens through several layers of clothing, such as nickel coins or phosphorus matches in pockets and leather shoe dyes through socks.  Arm-pit contact dermatitis is triggered by formaldehyde and perfumes in deodorants.  Paraphenylenediamine (PPD) added to darken Henna products is a potent skin sensitiser.  It is often found in the cheaper Henna-based skin tattoos and many hair products. Occasionally contact dermatitis may develop into a generalised “id reaction” or auto-eczematisation remote from the original area of contact.

Contact Urticaria

Contact urticaria is an IgE mediated “wheal and flare” reaction occurring within minutes of protein allergen skin contact. This is often seen with chefs (fresh shrimps & garlic) and animal handlers, as well as medical staff after latex rubber exposure.  Up to 10% of healthcare workers are now latex allergic and present with contact dermatitis, allergic rhinitis, asthma and even anaphylaxis.

Photosensitive dermatitis

Photosensitive dermatitis develops almost exclusively in males in sun exposure areas after ingestion of potential photo-toxins (psoralens) in foods (parsnip, celery, lime) and drugs (phenothiazines & diuretics) as well as topical sunscreens (para-aminobenzoic acid) and fragrances (musk) or Oil of Bergamot in cologne.

“Systemic” contact dermatitis

Systemic contact dermatitis is a controversial condition with a generalised or pompholyx-like eczemal dermatitis.  It affects mainly females who are nickel allergic on patch testing and have a chronic non-specific dermatitis.  It is suggested that the condition improves on a diet low in Nickel-containing foodstuffs and by avoiding nickel in cooking utensils.  Otherwise oral  Disulfiram (Antabuse) binds ingested nickel and so reduces the levels.

Identifying the cause:

Always have a high index of suspicion of occupational contact dermatitis in those workers dealing with food, detergents and solvents with frequent exposure to water, cleaning agents and oils.  Enquire about the exact nature of the occupation and chemicals in the workplace.  “What exactly does your job involve?”.  When do symptoms get worse and what alleviates them?  Enquire about trigger activities, hobbies, reactions to soaps or cosmetics, non-prescription creams and other cleaning agents.

Occupations most at risk for contact dermatitis include: Hairdressers, cement workers, food processors, florists, printers, chefs, builders, nurses, motor mechanics, painters, laundry workers, animal handlers and pharmaceutical factory workers.

Diagnostic Tests

Individuals react to a substance days after exposure; this is called a Delayed Hypersensitivity Reaction.  This delay in reaction time makes identification of the causative allergen very difficult.

Patch Testing is the cornerstone of diagnosing allergic contact dermatitis.  The various suspected allergens are placed on the skin (in Finn chambers) in a white soft paraffin base and kept in position for 48 hours (2 days).  The patches are then removed and the reactions assessed.  These are again reassessed after a further 48 hours (2 days), as irritant (but not allergic) reactions will disappear by this time.  Reactions are graded 0 (no reaction) to 3+ (redness with blistering) for each allergen. False positive results may occur with the “angry back” or “excited skin” syndrome of non-specific hypersensitivity.

Other specific allergen batteries are available for Face, Medicament, Steroid, Footwear; Hand & Hairdressing related contact allergens.

Another useful contact dermatitis test is the Open application test:  This involves applying the suspected allergen twice daily to the skin for a week. (Repeated Open Application Test (ROAT)).  Prick Tests are used to identify causes of Contact Urticaria.  Photopatch testing utilises UV-A light over test site to induce Photosensitive dermatitis

Management essentials:

A THOROUGH and ACCURATE ALLERGY HISTORY with PATCH TESTING followed by AVOIDANCE of implicated ALLERGEN and PROTECTION of SKIN with BARRIER CREAMS.

Avoidance of the implicated contact allergen is imperative as contact allergy is usually life-long.  Occupational contact dermatitis should be discussed with the employer and the worker relocated to a less exposed work-station.

Avoid all topical skin sensitisers such as antihistamine creams (mepyramine, antazoline, diphenhydramine), neomycin, benzocaine and tea tree oil.

Common Contact Allergens

Further reading.

1. Durham S., ABC of Allergies (BMJ 1998)
2. Holgate S, Church M eds.,  Allergy (Gower 1992)