Application of henna to the skin in order to achieve temporary tattooing is common practice in the Middle East and India. Traditionally, it is used by Muslims, Hindus and Jews as a decorative dye at weddings and other social events. Additional uses of henna include hair colouring and nail strengthening. Henna is also used in traditional medicine to treat alopecia, burns, headaches, gastrointestinal symptoms,3
and as an antimycotic, tuburculostatic and as ultraviolet-A blocker.2
Henna has the advantage of easy, quick and painless application as well as being temporary. Application of henna does not involve special tools and the risk of introducing infective agents to intact skin is null. However, henna tattooing is not completely safe. In children with glucose-6-phosphate dehydrogenase deficiency, life threatening hemolysis has been reported.6
Certain additives to henna preparations may cause an allergic adverse skin reaction. The most notorious agent is PPD. The classic reaction to PPD is consistent with Type IV delayed-type hypersensitivity reaction, however, an acute life-threatening Type I reaction has also been described.4
In most reported cases of the delayed type, henna was applied twice and it took a couple of days between the application and the development of a skin rash. In some reports the adverse skin reaction developed some weeks following the application.1
Patch tests to PPD were strongly positive.1,2,4,5
PPD cross-reacts with related compounds as sulfonamides, para-amino benzoic acid, sulfonureas, dapson, azo dyes, benzocaine and para-aminosalicylic acid. Therefore, people who are allergic to these substances may adversely react to PPD.7
The clinical presentations of allergic reaction to henna include erythema, swelling, blisters, weepy dermatitis, eczematous dermatitis, erythema multiform, lichenoid dermatitis, pruritic dermatitis and papular dermatitis. Although localised hypo-pigmentation is the most common consequence of the reaction, hyper-pigmentation was also described.2
The usual treatments for allergic contact dermatitis include application of topical corticosteroids and a short course of systemic antihistamines.1,2,4,5,7
Herbal psoralens (furocoumarins) applied to the skin may cause severe phytophotodermatitis when exposed to direct sunlight, which transforms the psoralens to quinones. Plants that are usually mentioned in this context are fig, celery, lime, lemon, parsley, carrot and dill belonging to the species Umbelliferae
, or Rutaceae
As some ‘secret’ ingredients of henna may include one of these substances and as henna tattooing is usually done on skin exposed to the sun, it is possible that some cases of henna dermatitis are in fact cases of phytophotodermatitis.
UV radiation-induced chemical changes, provoking an allergic skin reaction, can result not only from topical application to the skin. Systemic medications such as diuretics (hydrochlorothiazide, furosamide), antibiotics (tetracyclines, fluorquinolones, sulfonamides), chlorpromazine and nonsteroidal anti-inflammatory drugs may induce similar reaction.9
However, in this case, skin reaction will involve all sun exposed areas.
It is recommended that black henna should be avoided, especially in people who have had previous adverse reactions to henna, to certain medications or to hair dyes. Applying natural red-brown henna, without additives, and avoiding exposure of the tattoo to direct sunlight is usually safe, except in people with glucose-6-phosphate dehydrogenase deficiency. In a case of henna tattooing dermatitis, reaction to henna additives should always be considered.