Discussion
A recent article analyzing patch tests on 670 patients with their own products showed that hair cleansing products are a leading cause of contact dermatitis, third only to (1) medical products and (2) hair tints and bleaches.[4]
Fragrance, contained by 95% of the shampoos listed in the Walgreens database, was the most commonly found allergen. Fragrances are added to shampoos to increase marketability and customer appeal, and it is difficult to find a product that does not contain these allergens. Approximately 1 to 4% of the general population and 10% of the patch-test clinic population will have positive patch-test reactions to fragrances.[5,6] These percentage are increasing, possibly because of the increased use of fragrance-containing products.[7] It should be noted that owing to their transient contact with the skin surface, fragrances contained in shampoos are less likely to cause ACD than fragrances in leave-on products.[6] Nevertheless, those who experience ACD due to fragrance in shampoo are presented with a significant problem. One reason for this is that fragrances are considered trade secrets, and companies are not required to list the specific chemicals contributing to their aromas.[8] Therefore, patch-testing to elucidate which specific fragrance chemical is causing the reaction may be of low yield, and avoiding a specific chemical is very difficult without knowing which products contain it. In addition, the fragrance mixes that are currently used in patch testing yield a high number of false-positive reactions, and results should be interpreted with caution.[9] Of note, there are a limited number of shampoos that are fragrance free, and although they are difficult to find, they may offer options for those who are allergic to fragrance-containing products.
CAPB was found in 53% of the shampoos listed in the Walgreens database. CAPB is an amphoteric surface agent contained in many rinse-off products. There is some debate regarding the source of its allergic potential; the synthesis of CAPB is quite complicated, and many reactants and intermediates are found in the final product. Thirty patients with a known allergy to CAPB were patch-tested with varying impurities found in CAPB by Angelini and colleagues, who concluded that 3-(dimethylamino)propylamine (DMAPA), an intermediate in the manufacturing process, is responsible for CAPB allergy.[10] Other studies have suggested that amidoamine (AA) is the impurity causing CAPB allergy. Fowler and colleagues patch-tested 9 patients with known CAPB allergy with the manufacturing contaminants DMAPA, AA, and sodium monochloroacetate and found that 6 of the 9 patients reacted to AA whereas none reacted to DMAPA.[11] NACDG patch-test results from 2001 to 2002 indicated that 2.8% of the 4,913 persons tested had positive reactions to CAPB (although there is some question regarding the presence of AA, DMAPA, or both in some commercially available test allergens).
MCI/MI, a nonformaldehyde preservative commercially marketed as Kathon CG (Rohm and Haas Company, Philadelphia, PA), was present in 51% of the shampoos in the Walgreens database. This preservative has antifungal and antibacterial effects and is widely used in aqueous cosmetics and water-based personal care products.[12] Owing to its potential for chemical burns and membrane irritation and the fact that these reactions to the product are highly dependent on concentration and length of exposure, this preservative is now used in low concentrations and mostly in wash-off products.[13] A recent study determined that the elicitation threshold falls in the range of 2 parts per million (ppm).[14] The approved concentrations in the United States are 15 ppm for rinse-off products and 8 ppm for cosmetics; allergic reactions to MCI/MI at these concentrations are thought to be rare. The NACDG has determined that 2.3% of persons patch-tested with this product at patch-test concentrations of 100 ppm will have positive reactions.
Two other nonformaldehyde-releasing preservatives were used less commonly in shampoos: IPBC and MDBGN/PE rank as the ninth and tenth most common chemicals, being respectively present in 5.5% and 3% of the shampoos listed in the Walgreens database. IPBC is effective against fungal organisms and is a rare cause of contact allergy.[5] The NACDG found that only 0.3% of those patch-tested with this chemical will have positive reactions to it. In contrast, MDBGN/PE (listed also as Euxyl K400, Schülke & Mayr GmbH, Norderstedt, Germany), although found in only a small percentage of shampoos, is a significant source of allergic dermatitis. The NACDG found that 5.8% of patients will experience positive reactions to patch-tests with this compound. Interestingly, each chemical alone causes markedly fewer patch-test reactions; only 0.7% of patients react to MDBGN alone, and only 0.2% react to PE alone. Several articles have reported that most of the allergic potential stems primarily from MDBGN.[15] The authors of one such article found that 7 of 24 cases of severe hand dermatitis induced by MDBGN were caused by shampoo exposure, a reminder of the importance of considering ectopic locations of dermatitis.[16] The same authors concluded that MDBGN has enough allergic potential to make it unsuitable for use in any cosmetic product.[16]
DMDM hydantoin, diazolidinylurea, quaternium-15, and imidazolidinylurea are commonly used ingredients in shampoos; as a group, they were present in 49% of the shampoos in the Walgreens database. The NACDG found that DMDM hydantoin 1% in petrolatum caused positive reactions in 2.8% of patch-tested patients and that a 1% aqueous solution caused positive reactions in 2.2%. Diazolidinylurea caused a positive reaction in 3% of patch-tested patients, quaternium-15 resulted in a positive reaction in 9.3%, and imidazolidinylurea yielded a positive reaction in 3%. These formaldehyde-releasing agents inhibit the growth of microorganisms in cosmetics by slowly releasing formaldehyde over time. This extended time-release feature allows the concentration of free formaldehyde in the products to remain low and theoretically lowers the risk of contact allergy. Nevertheless, several studies have shown a high incidence of correlation between patch-test reactions to formaldehyde and to formaldehyde-releasing agents.[17] For example, de Groot and colleagues applied a cream that contained 1% DMDM hydantoin to 12 formaldehyde-allergic patients twice daily; 33% developed a reaction to DMDM hydantoin.[18] A similar study found an 81% rate of reactivity to formaldehyde in patients sensitive to diazolidinylurea.[19] Although these data imply a high risk of cross-sensitivity, this conclusion remains controversial, and some researchers suggest that sensitization to formaldehyde does not necessarily imply sensitization to formaldehyde-releasing agents. A recent study showed that when there is doubt, patch-testing with the individual preservatives is a reliable way of determining allergy to these products and also for determining which products a patient must avoid.[20]
Propylene glycol, a chemical solvent and emulsifying agent used in numerous household items, was found in 40% of the shampoos on the Walgreens list. It is used in a wide range of products, including cosmetics, food, toothpastes, and mouthwashes. In shampoo, it functions as a solvent and preservative.[21] There is some controversy regarding the allergic potential of propylene glycol. The NACDG found that 4.2% of individuals will have a positive patch-test reaction to it, but other studies have reported an incidence of positive reactions ranging from 0.1 to 3.8%.[3] This large variability may be due to the fact that propylene glycol is a strong irritant (the Material Safety Data Sheet advises avoidance of concentrations > 50%)[5]; therefore, patch tests may yield false-positive reactions. The NACDG currently uses 30% propylene glycol in water, a concentration that has significant potential for skin irritation.[21] At times, this irritation may be misinterpreted as contact dermatitis, leading to questionable data regarding the true allergic potential of the product. To verify positive patch-test results, Funk and colleagues suggested repeated patch tests with serial dilutions, biopsies of affected skin, and oral challenge tests,[21] but these methods are rarely used in the clinical setting.
Vitamin E (tocopherol) is used as an inexpensive and natural preservative in many cosmetics and hair care products. It is also sometimes added to beauty products because of the belief that it functions as an antioxidant and moisturizer. It was present in 28% of the shampoos found in the Walgreens database. Although tocopherol is generally believed to be a benign addition to many beauty products, it can occasionally cause allergic dermatitis. In fact, the NACDG reported that 1.1% of individuals who were patch-tested with dl-α-tocopherol experienced positive reactions. Case reports of tocopherol-induced dermatitis are relatively rare, but there are reports of widespread dermatitis following localized application.[22] In addition, a large-scale report of dermatitis induced by vitamin E described an outbreak of papular and follicular dermatitis that occurred in Switzerland following the introduction of a new cosmetics line.[23] Perrenoud and colleagues patch-tested 77 of these patients and found that the agent responsible for the outbreak was tocopherol lineolate.[23] With this data in mind, they concluded that oxidized vitamin E derivatives may be responsible for irritation from many cosmetic products.
Dermatitis. 2009;20(2):106-110. © 2009 American Contact Dermatitis Society
Cite this: Shampoos - Medscape - Mar 01, 2009.
