Allergens in Popular Hair Products May Cause Allergic Contact Dermatitis

Certain allergens in hair care products may cause allergic contact dermatitis (ACD) in some patients, resulting in eczematous lesions and swelling in the rinse-off distribution at the nape of the neck, retroarticular area, hairline, eyelids, ears, and lateral face, according to authors of a review published in Dermatitis.

The researchers sought to evaluate common hair care practices and product ingredients that may cause ACD. Based on their findings, they offered practical tips for identifying allergens, advocating for patch testing as the gold standard of diagnostic confirmation.

Scalp presentation of ACD can include dermatitis, edema, burning, pruritis, hair shedding, or pain. In some cases, however, possibly owing to a region of immune tolerance created by the high concentration of regulatory T cells surrounding hair follicles, the scalp may be spared and ACD, instead, presents in the “rinse-off” area (the neck and lateral face). Shampoos (including antidandruff shampoo) and conditioning products are often associated with neck and lateral face dermatitis. Potential allergens (fragrances, adhesives, dyes, emulsifiers, surfactants, and preservatives) can be found in hair dyes—including coloring, bleaching, and lightening products—waxes, oils, hair gels, hairsprays, minoxidil solution and foam, and topical steroids applied to the scalp.

The most common allergens associated with contact dermatitis from hair care products are paraphenylenediamine (PPD), an ingredient in permanent hair dye that can cause marked hypersensitivity reactions, including eczematous plaques, followed by methylisothiazolinone (MI) and methylchloroisothiazolinone (MCI), preservatives commonly found in shampoos.

In addition, formaldehyde-releasing preservatives are used in many shampoos. Formaldehyde concentrations up to 2000 ppm are permitted in shampoos and cosmetic products. Conversely, formaldehyde-free keratin treatments can still release formaldehyde at levels exceeding occupational exposure limits. Reported symptoms of ACD caused by hair products containing formaldehyde (which is most frequently used in hair-straightening treatments) can occur within 24 hours of exposure; symptoms include edema of the scalp, face, and periorbital regions, and eczematous eruptions.

Ethnicity and hair morphology may have an impact on baseline hair strength and individual hair care practices, in turn influencing the specific allergens to which different patients are exposed. For instance, black individuals and people with coiled hair or tight curls are at higher risk of developing ACD since natural oils cannot migrate down coiled hair as easily as down straight hair, thus increasing the risk of scalp desiccation and seborrheic dermatitis. In addition, infrequent hair-washing, due to increased dryness after washing, may contribute to this dermatitis.

Decyl glucoside (a surfactant and the most common glucoside allergen identified by patch testing) is known to be less drying and so is commonly found in shampoos for ethnic hair. It is listed as an ingredient in close to 45% of hair products targeted toward those with ethnic hair vs 11% of products for those with nonethnic hair. Decyl glucoside is an important allergen for clinicians to consider among Black patients and those with coiled hair/tight curls who present with ACR.

Patients may also present with ACD as a result of using henna products that contain PPD. Patients who have (or are suspected of having) allergies to PPD might opt to use dyes without this ingredient. A spot test or allergy alert test to determine tolerance can be administered before the patient uses a new hair dye.

In an investigation of the frequency of positive patch tests in nearly 19,457 patients, PPD was found to be a more significant allergen among Black (7.0%) vs White patients (4.4%).

Among commonly used oils for hair (such as tea tree, peppermint, rosemary, and thyme oil), tea tree oil has been cited most frequently as a cause of ACD. Tea tree oil has been identified as an ingredient in 2.8% of products targeted toward ethnic hair and in 5.3% of products targeted toward nonethnic hair. The allergic reaction often occurs as a result of application of pure oil (although ACD can also be caused by shampoos, soaps, and shaving cream containing this ingredient). It is generally due to oxidation that forms peroxides, endoperoxides, and epoxides. Therefore, oxidized tea tree oil should be a considered allergen in patch testing.

Certain scalp and skin presentations can result from allergic reactions to specific irritants. For example, patients with an allergic response to the nickel sulfate commonly used in hair accessories may present with localized dermatitis. Patients with a PPD allergy may often present with a reaction to thioglycolates found in permanent wave products. Patients, especially atopic patients, with irritation caused by adhesives/glues (acrylates) in hair extensions and prosthetic/synthetic hair pieces (wigs) may present with dermatitis; the dermatitis is usually localized to the area of applied adhesive, and patients may present with pruritic eruptions on the neck (negative patch tests) and/or eczema and periorbital edema.

“Patients presenting with eczematous lesions or edema of the scalp, face, eyelids, or in the ‘rinse-off’ distribution should be suspected of having ACD from hair care products,” the authors concluded. They added, “In reviewing a patient’s risk for ACD, dermatologists should inquire about hair care practices, styling methods, and review ingredients in hair care products. Patch testing is the gold standard for detecting such allergens.”

Disclosure: Some study authors declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of authors’ disclosures.

References:

Karim M, Klein EJ, Nohria A, et al. Potential for allergic contact dermatitis in popular hair care practices and ingredients. Dermatitis. Published online June 20, 2023. doi:10.1089/derm.2023.0045