Allergic Contact Dermatitis of the Scalp: What are the top causes?

Hair Dyes, Shampoos and Conditioners Top the list of Hair Products Causing Allergy

Anything that is applied to the scalp has the potential to cause an irritant contact dermatitis (ICD) or allergic contact dermatitis (ACD). Irritant contact dermatitis can happen after a single exposure whereas allergic contact dermatitis (ACD) requires repeat exposure in order for the immune system to mount a response. ICD is more common than ACD. Some ingredients rarely cause any type of allergic reaction, whereas others are much more likely.

Pham et al, 2022

Authors recently set out to evaluate the published medical literature to identify some of the products most likely to cause allergic contact dermatitis. The authors identified 99 studies with a total of 3185 patients. Scalp products were divided into 31 categories.

The most common symptoms were eczema followed by redness.

The hair products that were most likely to cause ACD were hair dyes (41%), shampoos (28%), and conditioners (22%). The actual allergens that were most likely were p-phenylenediamine (23%), nickel (15%), fragrance mix (13%), balsam of Peru (10%), cocamidopropyl betaine/3-dimethylaminopropylamine (7%), and methylchloroisothiazolinone/ methylisothiazolinone (6%).

When it came to shampoos, I noted that the most commonly reported surfactants in shampoos causing scalp ACD were cocamidopropyl betaine (n = 34) and cocobetaine (n = 2). I found it quite interesting that one of the most common nonsurfactant ingredient was the antidandruff ingredient zinc pyrithione.

Most patients with scalp ACD were found to have some sort of involvement of the face or eyelids or ears or neck. In fact, for patients with some sort of scalp ACD, 17% had only the scalp involved whereas 83 % had some other area also involved. 21 % had involvement of the face, 18 % had the neck involved, 12 % had forehead involvement and 9% had chest, 8 % had ears and 8% had eyelids.

The authors remind us that products like headbands, wig adhesive, CPAP machine straps, spectacle frames and hats can be allergens too

Conclusion:

We always need to be thinking about contact dermatitis in patient with scalp itching, burning and redness. In addition, we need to ask about redness and scaling on so called “rinse off areas” of the face, forehead, ears, upper eyelids, and neck as these are common sites. It’s rare actually in the case of a true ACD for the scalp to be affected but the skin of the neck, ears, eyelids be unaffected. So if one is thinking that scalp redness and scale is due to some kind of ACD, it’s really helpful to evaluated the face, eyelids, ear and neck.

Hair loss can sometimes occur with ACD but is not so common. Hair loss is common for example with ACD to hair dyes.

It’s not surprising that hair dyes are at the top of the list givne that 75 % of US women use hair dyes.

It’s interesting that antidandruff shampoo ingredients like zinc pyrithione can rarely be a problem. Clearly any patient whose seborrheic dermatitis does not improve on zinc pyrithione needs to change shampoos. Fortunately ACD is rare to antidandrufff shampoos with these ingredients.

REFERENCE

Pham et al. Allergic Contact Dermatitis of the Scalp Associated With Scalp Applied Products: A Systematic Review of Topical Allergens. Dermatitis. 2022 Mar 22.