Allergens are substances that can cause an allergic reaction, that is, hypersensitivity in contact with them, since the body recognizes them as foreign, then an immune system response is produced.

The most common allergens come from animals, such as hair or feathers, but we also find compounds that can cause allergic reactions in food, and even cosmetic products.

Allergens in cosmetic products

Allergic responses to cosmetic products are not frequent, being contact dermatitis the most common manifestation. A study carried out at the General University Hospital of Valencia determined that the incidence of contact dermatitis with cosmetic products had increased from 9.8%, calculated between 1996 and 2004, to 13.9% in the period between 2005 to 2013 [1].

The most allergenic substances are fragrances, of which there are 26 allergenic ingredients whose declaration is mandatory on the labelling of cosmetic products. In fact, regulation (EC) 1223/2009 includes the minimum concentration by which these substances must appear indicated on the label.

In addition to fragrances, there are other types of cosmetic ingredients that can cause an allergic reaction, such as: preservatives such as methyldibromoglutaronitrile, formaldehyde, and Kathon CG. Antioxidants, such as BHA or BHT, excipients such as dicaprylyl maleate, parabens, and hair dyes with the presence of p-phenylenediamine [2].

Allergens in makeup and nail products

In formulations such as nail polish, the most allergenic ingredient is formaldehyde resin. In fact, it is estimated that toluene sulfonamide causes sensitization in 4% of users. On the other hand, artificial nails also contain methacrylates, such as EGDMA or 2-HEMA, which can cause eczema on the skin [2].

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Makeup products such as lipsticks, shadows or eyeliner may contain substances that, in certain people, cause allergic reactions. This is the case of euxyl K-400, kathon and balsam of Peru in makeup powders. Propyl gallate, octyl gallate and mercury in lipsticks, nickel sulfate in eye pencils and Thiomersal used in eye shadows [3].

Allergens in sunscreens

Sunscreens contain ingredients that can cause allergic reactions and contact dermatitis such as benzophenones or para-aminobenzoic acid. However, sensitization to this type of products is considered low, below 1% [2].

We should not confuse contact dermatitis with the so-called “sun allergy”, which we talked about in a previous post. The rashes or irritations after sun exposure that we know as sun allergy are usually caused using certain medications in conjunction with sun exposure, which causes  photodermatosis.

Natural cosmetics can also present allergens

There is a widespread belief that formulating cosmetic products with natural ingredients makes these products safer or less allergenic than non-natural ingredients.

However, a study conducted with natural cosmetic products marketed in the United States revealed that the 1,651 products analysed contained an average of 73 different allergens according to the list of ingredients that commonly cause contact dermatitis, made by the American Contact Dermatitis Society.According to this same study, the most allergenic natural ingredients would be fragrances from lavender and other botanical extracts. [4].

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Cosmetic ingredients, whether of natural or synthetic origin, are monitored and regulated by health authorities. The European Commission regulation No. 1233/2009 includes all the substances that cannot be used in the manufacture of cosmetics. In the next revision of said regulation, an expansion of these substances is expected to 60 additional substances as allergens. In fact, some essential oils have been banned or restricted because they contain molecules that can cause unwanted skin reactions such as irritation or allergic reaction.

Could a cosmetic product cause an allergy?

As we have indicated at the beginning, allergic reactions to cosmetic ingredients are not frequent. People with sensitive skin or dermatitis are more susceptible to allergic reactions in contact with cosmetic products, so it is advisable to monitor the ingredients of the products, perform a test on a small portion of the skin and consult a specialist in case of doubt.



  1. Zaragoza-Ninet, V., Blasco Encinas, R., Vilata-Corell, J. J., Pérez-Ferriols, A., Sierra-Talamantes, C., Esteve-Martínez, A., & de la Cuadra-Oyanguren, J. (2016). Allergic contact dermatitis due to cosmetics: A clinical and epidemiological study in a tertiary hospital. Dermatitis alérgica de contacto a cosméticos, estudio clínico-epidemiológico en un hospital terciario. Actas dermo-Sifiliograficas, 107(4), 329–336.
  2. González-Muñóz, P., Conde-Salazar, L., Vañó-Galván, S. (2014). Dermatitis alérgica de contacto a cosméticos. Actas dermo-Sifiliograficas, 105 (9), 822-832.
  4. Young, P. A., Gui, H., & Bae, G. H. (2022). Prevalence of Contact Allergens in Natural Skin Care Products From US Commercial Retailers. JAMA dermatology, 158(11), 1323–1325. Advance online publication.

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