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Dr Helen Horn and Anne Smith advise on identification of triggers and successful management
Contact dermatitis is common and should be considered when managing any acute, chronic or recurrent dermatitis. Both the distribution and time course help to distinguish between the different types of contact dermatitis and to differentiate them from endogenous eczemas such as pompholyx, atopic eczema or seborrhoeic eczema.
Irritant contact dermatitis
Irritant reactions account for 80 per cent of all contact dermatitis2 and typically affect the face or hands. Acute reactions occur following a single overwhelming exposure to damaging irritants such as bleach or chemicals but repetitive contact with one or more weaker irritants causes low-grade chronic inflammation and prevents recovery.
Dryness, redness, scaling and minor fissuring of chronic irritant hand eczema, affecting the dorsum of the hand and extending into finger webs indicate repeated exposure to water and inadequate drying of the hands. Hyperkeratotic and fissuring chronic irritant hand dermatitis usually affect both hands, are painful and can cause permanent disability.
Irritant contact dermatitis is most prevalent in mothers of young children, atopics who suffered from hand eczema during childhood and in those whose occupations expose them to frequent or prolonged contact with water.
Allergic contact dermatitis
Allergic contact dermatitis occurs when the skin comes into contact with substances which have previously sensitised the immune system. Onset of symptoms is usually delayed until six to 48 hours later type IV cell mediated delayed hypersensitivity but in type I IgE reactions, itch and urticaria occur within 30 to 60 minutes.
The diagnosis of type IV contact allergy is confirmed by patch testing. Patch tests are not helpful for the investigation of type I allergies or urticaria and cannot be applied to areas of active eczema or to skin that has recently been exposed to ultraviolet light.
All patients undergoing patch testing should have the British Contact Dermatitis Society standard battery of allergens applied to their upper back for 48 hours. Results are read both when patches are removed and again 48 hours later. It is often appropriate to apply additional allergens. Irritant patch test reactions are common. Experience is necessary to distinguish them from allergic reactions.
Temporary henna tattoos can sometimes cause allergic reactions. Allergy is caused not by the henna but by para-phenylenediamine (PPD) or essential oils added to modify the colour5. Patients sensitised to PPD must be warned to avoid hair dyes that can cause severe dermatitis.
Type IV contact allergies to topical treatments and components of dressings are especially common in leg ulcer patients.
Allergy to natural rubber latex (NRL) can cause anaphylaxis perioperatively or during dental procedures. Radioallergosorbent (RAST) testing for specific IgE antibody to latex is positive in 75 per cent but in the remainder, short contact, prick testing or a use test will confirm the diagnosis.
Resuscitation facilities must be available when these tests are undertaken.
Following the introduction of better-quality non-powdered latex gloves, the incidence of latex allergy appears to be decreasing6.
Treatment of contact dermatitis
Although topical treatments are important, contact dermatitis will persist unless irritants and allergens are successfully identified and avoided. Emollients offer protection and should be re-applied frequently.
Hands can be conveniently protected by cotton gloves with PVC gloves over these for wet tasks, but formal dressings, which are less easily removed, are more effective.
Sufficiently potent topical steroid ointments should be used on inflamed areas, reserving steroid creams (which contain preservatives) for short-term use on weeping skin.
Helen Horn is associate specialist in dermatology, and
Anne Smith is a dermatology nurse practitioner, both at the Royal Infirmary of Edinburgh
1 Bourke J et al (2001) Guidelines for the management of contact dermatitis. Br J Dermatol
145 (6): 877-85
2 Marks JGD, Marks VA (1997). Contact and occupational dermatology. 2nd edn. Mosby, London
3 Meding B, Jorvholm B (2002). Hand eczema in Swedish adults changes in prevalence between 1983 and 1996.
J Invest Dermatol 118:719-23
4 Goh CL (1999) Irritant contact dermatitis. In: English JSC, ed. Colour handbook of occupational dermatology. Manson Publishing, London: 11-29
5 Temesvari E et al (2002). Fragrance sensitisation caused by temporary henna tattoo. Contact Dermatitis 47 (4):240
6 Chowdhury MM, Statham BN (2003). Natural rubber latex allergy in a health care population in Wales.
Br J Dermatol 148:737-40
The British Allergy Foundation
Latex Allergy Support Group
National Eczema Society
Information line 0207 561 8230