The scalp often comes into contact with various potentially allergenic compounds, which in many cases can lead to contact allergic dermatitis. Potentially allergenic compounds can be various substances also found in cosmetic products for hair and scalp care. How susceptible we are to developing contact dermatitis depends on each individual's immune system. Allergenic substances do not only come into superficial contact with the skin but penetrate deeper, all the way to the hair follicles. In addition to the mentioned cosmetic products, the main sources of allergies in correlation with the scalp are primarily topical, scalp-specific medications such as minoxidil, anti-seborrhea preparations, and local steroids. Understanding the onset of an allergic reaction on the scalp is crucial for your self-confidence and the choice of products for hair care and nourishment. We will guide you through an introduction to allergic contact dermatitis, its most common triggers, and the relief of its symptoms.
What is Allergic Contact Dermatitis (ACD)?
Allergic contact dermatitis is divided into two subgroups: irritant and allergic. Irritant contact dermatitis is a non-specific, non-immunologically induced body response to chemical compounds or physical factors that disrupt or irritate the epidermal skin barrier. Allergic contact dermatitis, however, is characterized by an association with a hypersensitive reaction of the body's immune system. The reaction occurs when an individual is exposed to a certain substance to which they have not previously developed specific immune system insensitivity. When using hair and scalp care products, allergic contact dermatitis is not uncommon. The most common symptoms are various conditions of dry, damaged, irritated, and inflamed skin, which can be caused by contact with certain substances in these products. Allergic contact dermatitis occurs with an immune response to allergens, the skin becomes itchy, blistered, dry, and cracked. Lighter skin turns red, darker skin turns brown, purple, or gray. Upon exposure to allergens, such a condition can appear after a few hours or even days, and the condition of ACD can improve or even heal if we identify and avoid the substance causing the mentioned problems.
Common Allergens Causing ACD
Allergens are an interesting topic. We know some general allergens with high allergenic potential, but most of them we don't. Why? People have different organisms, their own unique immune systems, and there is no general rule about allergenic substances. One person is allergic to one substance, another to another, and so on. In hair care and washing cosmetics, we know some products with significantly higher allergenic potential. The range of these products is quite wide. Hair dyes and bleaches are at the top of this list, followed by perming and hair straightening preparations, then preservatives in shampoos and conditioners, foaming agents, perfumes, and essential oils… We must not forget hair masks, lotions, topical medications, and even sunscreens.
Hair Dyes
As mentioned, hair coloring preparations account for the vast majority of ACD cases on the scalp. Almost all dyes contain paraphenylenediamine (PPD) or its derivatives. It is found in permanent and semi-permanent hair color products and is the main cause of hypersensitivity among the compounds in these products. Research has shown that people from Southern European countries are more exposed to allergic contact dermatitis induced by PPD. The severity of the allergic reaction also depends on the type of dyes, their permanence, and the application time.
(Source: Diseases of the Hair and Scalp. Medical, Surgical, and Cosmetic Treatments, Second Edition)
Permanent Hair Waving
There are three types of permanent waves: cold, acidic, and neutral. Glyceryl monothioglycolate, found in acidic perming preparations, is the most common cause of scalp ACD among chemicals for permanent hairstyles. Improper use of ammonium thioglycolate in cold perm solutions causes extensive hair breakage and a severe irritant reaction. Despite the aggressiveness, allergic reactions are less common. Most "acidic" permanent wave products contain glyceryl monothioglycolate, which is a severe allergen. Reports indicate that this compound causes ACD and contact urticaria (itchy rashes on the scalp). The compound is particularly problematic because it can remain on the hair for up to three months after application. Cysteamine hydrochloride is an active chemical for neutral permanent waves. The neutral perming process is less harmful, as reactions in a relatively neutral pH rarely occur. This process is an alternative for all individuals hypersensitive to glyceryl monothioglycolate. Most unwanted side effects of this neutral process are associated only with irritant reactions.
Shampoo and Conditioner
The allergenic potential of shampoo is extremely small due to the fact that it is in contact with the scalp for only a short time and is also diluted with water during use. Nevertheless, hypersensitivity to shampoo is not uncommon, especially when the shampoo contains cocamidopropyl betaine.
Common surfactants include cocamidopropyl betaine, amidoamine, DMAPA, oleamidopropyl dimethylamine, decyl glucoside, and lauryl glucoside. Shampoos often also contain fragrances, preservatives, and anti-dandruff agents (zinc pyrithione, selenium sulfide, and even tea tree oil). All these raw materials can cause allergies.
Conditioners, unlike shampoos, are an insignificant cause of contact allergy on the scalp. However, hydrolyzed proteins or panthenol in conditioners, especially in people with atopic dermatitis, can trigger contact urticaria. Similar to shampoos, fragrances and preservatives can be considered potentially allergenic components.
Leave-in Hair Products
Hair sprays allow styling by applying a thin film of polymer around the hair. Styling mousses are similar. Styling gels are composed of a polymer and a thickener; they can also contain raw materials for a shiny hair appearance. Preservatives, fragrances, and dyes in these products are also potentially allergenic.
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