Hair dye reactions are usually caused by allergic contact dermatitis to the dyeing agents, which are classed as aromatic amines. These are powerful allergens. The usual patch test screening agent for hair dye allergy is p-phenylenediamine (ppd) which is used in patch testing at a concentration of 1 % pet. Hair dye contact allergy may occur in 1 % of the normal population in some countries and is commoner with increasing age. Hair dye allergy usually presents as an acute dermatitis on the head and neck, more pronounced on the skin off the scalp. Severe reactions can mimic angioedema. However allergic contact dermatitis to hair dye can present in a variety of ways, such as lichenoid dermatitis, pigmented dermatitis or even erythema multiforme. A delayed reaction to temporary ‘henna’ tattoo represents an active sensitisation reaction to hair dye chemical. Occupational cases with hand dermatitis in hairdressers often occur early in the patients’ career. Type 1 hypersensitivity to hair dye is a rare but potentially serious adverse reaction. As the hair dyeing process is alkaline, irritant reactions can occur. If hair dye allergy is suspected but the PPD patch test is negative, testing to other aromatic amines may be useful.
Keywordsp-Phenylenediamine Toluenediamine Hair dyes Allergic contact dermatitis Patch testing