This type of dermatitis is caused by a true allergy to a particular substance and is detected by patch testing. Various substances are applied to the skin, left on for forty-eight hours, and then checked for reactions. Given that we are exposed to so many different chemicals, contact allergic dermatitis is surprisingly rare. The most common causes are as follows:
Cosmetics contain at least ten substances which can produce allergic reactions. The most common of these is perfume, but preservatives, which are used in all cosmetics (even so-called ‘natural’ cosmetics), are also frequently to blame. The most commonly used preservatives include Dowicill (Quanternium 15), Germall (Imidazoyl urea), Kathon (methylchloro-isothiozalone) and parabens. All cosmetics manufacturers are now required to list the ingredients of their products on the labels so that people can tell which cosmetics they are able to use. With the increased interest in ‘natural’ cosmetics many plant extracts are now being included in cosmetics. Plant extracts such as aloe vera, however, can also cause allergic reactions.
Perfumes contain many chemicals, often numbering thirty or more. These are present not only in actual perfumes, but in most cosmetics and even some medicinal creams. Perfumes are used to mask the chemical smell of cosmetics, thus making them more attractive to consumers. Perfume allergy can produce dermatitis on the eyelids, neck and face. Some cosmetic ranges, such as Almay, Clinique and Innoxa, are not perfumed, and so may be safely used. If you are allergic to perfume it should not be applied directly onto the skin but can be applied to clothing instead.
Hairdressers are particularly prone to contact allergic dermatitis from hair dye, as are those who have their hair dyed. Hair dye rarely causes dermatitis of the scalp itself, but rather around the scalp margin and on the eyelids. If contact dermatitis develops to a particular hair dye, another colouring agent should be used. Contact allergic dermatitis can also be caused by perming solutions.