Fragrance ingredients are the most frequent culprits in cosmetic allergies [11-15]. Katsarar et al., who investigated the results of patch testing over a 12-year period, found an increasing trend in sensitivity to fragrance compounds, which reflects the effectiveness of the advertising of perfumed products . Common features of a fragrance contact dermatitis are localization in the axillae, localization on the face (including the eyelids) and neck, and well-circumscribed patches in areas of dabbing-on perfumes (wrists, behind the ears) and hand eczema or its aggravation. Airborne or connubial contact dermatitis should be considered as well.
Sensitization is most often induced by highly perfumed products, such as toilet waters, aftershave lotions, and deodorants, the last of which have recently been shown to contain well-known allergens such as cinnamic aldehyde and iso-eugenol .
Table 1 Cosmetic and Cosmetic-Related Dermatitis Caused by Direct Application of the Allergen
Area of dermatitis Cosmetics that may contain allergens
Face in general
Forehead Eyebrows Upper eyelids
Lower eyelids Nostrils
Lips, mouth, and perioral area
Neck and retroauricular area Head
Trunk/upper chest, arms, wrists
(elbow flexures) Axillae
Anogenital areas Hands
Facial skincare products (creams, lotions, masks), sunscreen products, makeup (foundations, blushes, powders), cleansers (lotions, emulsions), and cosmetic appliances (sponges), perfumed products (after-shave lotion) Haircare products (dyes, shampoos) Eyebrow pencil, depilatory tweezers Eye makeup (eye shadow, eye pencils, mascara), eyelash curlers Eye makeup Perfumed handkerchiefs
Lipstick, lip pencils, dental products (toothpaste, mouthwash), depilatories Perfumes, toilet waters, haircare products Haircare products (hair dyes, permanent-wave solutions, bleaches, shampoo ingredients), cosmetic appliances (metal combs, hairpins) Haircare products, perfume
Bodycare products, sunscreens and self-tanning products, cleansers, depilatories Deodorants, antiperspirants, depilatories Deodorants, moist toilet paper, perfumed pads, depilatories Handcare products, barrier creams, all cosmetic products that come in contact with the hands Footcare products, antiperspirants
As reported in the literature, the fragrance mix remains the best screening agent for contact allergy to perfumes because it detects some 70 to 80% of all perfume allergies [19,20]. However, additional perfume-allergy markers are certainly needed.
Preservatives are second in frequency to fragrance ingredients; they are important allergens in cleansers, skincare products, and makeup [12,21]. However, within this class important shifts have occurred over the years.
The methyl(chloro)isothiazolinone mixture was commonly used in the 1980s and was then a frequent cause of contact allergies. This frequency has declined considerably in recent years [3,12]. Since then, formaldehyde and its releasers—particularly methyldi-bromoglutaronitrile (=dibromodicyanobutane) as used in a mixture with phenoxyethanol, better known as EUXYL K400—did gain in importance in this regard [12,21-25], although the frequency of positive reactions observed seems to be influenced by the patchtest concentration [24,25].
The spectrum of the allergenic preservatives also varies from country to country. For example, in contrast to continental Europe where reactions to methyl(chloro)isothia-zolinone and more recently methyldibromoglutaronitrile have been the most frequent, [12,13,21,26], in the United Kingdom formaldehyde and its releasers have always been
much more important, particularly as concerns quaternium-15  although its incidence seems to have recently slightly decreased . Parabens are rare causes of cosmetic dermatitis. When a paraben allergy does occur, the sensitization source is most often a topical pharmaceutical product, although its presence in other products can be sensitizing as well . Recently, we observed such a case (data on file): a young lady, after having previously been sensitized to mefenesin in a rubefacient, presented with an acute contact dermatitis on the face at the first application of a new cosmetic cream containing chlorphenesin, which was used as a preservative agent. Apparently it is a potential sensitizing agent  and probably cross-reacts with mefenesin, which is used in pharmaceuticals.
Antioxidants form only a minor group of cosmetic allergens. Examples are propyl gallate, which may cross-react with other gallates and are also used as food additives, and t-butyl hydroquinone, a well-known allergen in the United Kingdom but not in continental Europe .
"Active" or Category-Specific Ingredients
With regard to ''active'' or category-specific ingredients, in contrast to de Groot  we found an increase of the number of reactions to oxidative hair dyes (PPD and related compounds) during the period 1991-1996 compared with the period 1985-1990 [12,13]. According to one cosmetic manufacturer (personal communication, L'Oréal, 1997), the use of such hair dyes has more than doubled in recent years. However, the replacement since 1987 of PPD-hydrochloride by PPD-base—a more appropriate screening agent for PPD-allergy—may also have influenced the incidence . They are important causes of professional dermatitis in hairdressers, who also often react to allergens in bleaches (persulfates, also causes of contact urticaria), permanent-wave solutions (primarily glycer-ylmonothioglycolate, which may provoke cross-sensitivity to ammoniumthioglycolate), and sometimes shampoos (e.g., cocamidopropylbetaine and formaldehyde) [31,32]. Sodium pyrosulfite (or metabisulfite), present in oxidative hair dyes (data on file), was recently also found to be a professional allergen.
Tosylamide/formaldehyde (=toluenesulfonamide formaldehyde) resin is considered an important allergen  and is the cause of ''ectopic'' dermatitis attributable to nail lacquer, which may also contain epoxy and (meth)acrylate compounds . It often gives rise to confusing clinical pictures and may mimic professional dermatitis .
(Meth)acrylates are also causes of reactions to artificial nail preparations, more recently to gel formulations, in both manicurists and their clients .
Moreover, some more recently introduced ''natural'' ingredients may induce contact-allergic reactions. Some examples are butcher broom (Ruscus aculateus), which is also a potential allergen in topical pharmaceutical products , hydrocotyl (asiaticoside) , and dexpanthenol . Farnesol, a well-known perfume ingredient and cross-reacting agent to balsam of Peru, has become a potential allergen in deodorants in which it is used for its bacteriostatic properties .
Some sunscreen agents such as benzophenone-3, which may also cause contact urticaria, and dibenzoylmethane derivatives have been recognized in the past as being important allergens [3,21,39-41]. Indeed, isopropyldibenzoylmethane was even withdrawn for this reason . Methylbenzylidene camphor, cinnamates, and phenylbenzimidazole sul-
fonic acid are only occasional, sometimes even rare, causes of cosmetic reactions. The use of para-aminobenzoic acid (PABA) and its derivatives has decreased considerably. Contact allergic reactions to them were generally related to their chemical relationship to para-amino compounds , although they were also important photosensitizers .
In our experience [12,13,21], the contribution of sunscreens to cosmetic allergy is relatively small despite the increase in their use because of media attention being given to the carcinogenic and accelerated skin-aging effects of sunlight. The low rate of allergic reactions observed may well be because a contact allergy or a photoallergy to sunscreen products is often not recognized, since a differential diagnosis with a primary sun intolerance is not always obvious. Furthermore, the patch-test concentrations generally used might be too low , in part because of the risk of irritancy.
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