Skin Allergies: We Are Not Born Allergic, We Become Allergic

You may have thought you were taking good care of your skin by choosing fragrance-free products to avoid an allergic skin reaction. And then, one day, you suddenly develop an itchy rash. Rest assured that yours is not an isolated case: 10% to 20% of the world’s population experiences an allergy-related irritation to a cosmetic ingredient^1,2,3. The WHO even estimates that this number is expected to rise⁴, particularly in industrialized countries, where there are now almost 3 times as many skin reactions compared with 1996^5,6.

In this article, we will focus on the ingredients in cosmetic products that can trigger skin allergies. What causes these allergic reactions? Which ingredients should be avoided and what are some tips for choosing the right cosmetic products?

Allergist Séverine Fernandez shares her expertise on the subject.

Allergies: why does our body rebel against certain substances?

An allergic reaction is an inappropriate response of the immune system to a normally harmless environmental substance (the allergen). The body sees the allergen as a threat, like bacteria or a virus, and decides to fight it off with an overreaction.

There are many types of allergens: foods, cosmetic ingredients, pollen, mites, etc. However, bear in mind that the body’s defense mechanism when your skin breaks out in spots or pimples after applying a face cream is by no means comparable to a food allergy to peanuts⁷.

Mechanism of action: the calm before the storm

One thing that all allergies have in common is their mode of action, which occurs in two stages:

• Initially, there is a period during which we are repeatedly exposed to an allergen. We experience no symptoms, so we assume that everything is fine.Meanwhile, our immune system has already mistakenly perceived this chemical as an enemy. This is the sensitization phase.
• Then, after a certain period of time, which varies from person to person, the body can no longer tolerate contact with this supposed enemy. The body will now produce a reaction every time it is exposed to the antigen. This is the elicitation phase⁸.

Skin allergies are linked to a specific type of immune cells: attacking white blood cells⁹. When the allergen is reintroduced into the body through a cosmetic product, these attacking white blood cells are summoned as reinforcements. They are activated, multiply, and release chemical compounds that trigger skin lesions. Their goal is to destroy the invading allergen at all costs. Unfortunately, this reaction also induces a rash and skin inflammation.

One of the peculiarities of skin allergies is that it is not impossible to develop allergies to several ingredients. This is because various plant extracts may contain the same allergen. For example, it is common to be allergic to geranium and rose essential oils because they both contain geraniol¹⁰, a compound on the European Union’s list of allergenic fragrances¹¹.

Symptoms that are no fun

After the silent sensitization phase, – which can last several months, years or even decades, – each subsequent exposure will trigger a skin reaction within 24 to 72 hours. This can result in various symptoms such as severe itching, redness, swelling, dry skin, the appearance of small blisters, etc⁷. Ouch!

In addition, the symptoms of a skin allergy can typically worsen over time and become increasingly rapid in onset. After several exposures, some attacking white blood cells will remain present in the skin, at the point of usual contact with the allergenic cosmetic (particularly on the hands, face, and armpits). They are standing by, ready to spring into action at the next encounter⁸. This explains why symptoms can worsen over time and appear in less than 24 hours.

These allergy symptoms should not be confused with irritation, another unpleasant and annoying skin reaction. The latter is a temporary injury to the skin or eyes caused by a substance with corrosive properties. The reaction can occur rapidly and varies based on each individual’s skin resistance and the concentrations used in cosmetic products. This creates a pulling and burning sensation, rather than itching⁷. Conversely, it is important to remember that an allergy is caused by your body’s overreaction to a harmless substance, even if it is present in very small quantities!

It is therefore easy to understand why it is so important to check for the presence of potential allergens in our cosmetic products, even if we experience no symptoms. The idea is to ensure that your body does not encounter these substances so that, in the future, it will not recognize them as a threat. This is because, once your body’s immune system becomes sensitized to an allergen, there’s no turning back!

Are some people more sensitive than others?

Anyone can suddenly become allergic to a substance, and at any age. However, certain predispositions and environmental phenomena can promote the triggering of this reaction.

Firstly, it is important to remember that damaged skin opens the door to external aggressors. Allergens find it easier to penetrate into barrier-disrupted skin and attach themselves to immune system cells. That is why people with skin conditions, or those who have suffered from skin diseases during childhood, are more likely to develop an allergy later in life. It should be noted that atopic dermatitis, an inflammatory skin disorder affecting 10% of children worldwide, tends to promote a higher prevalence of this sensitization to allergens¹².

Another important fact: skin composition varies from person to person. On the surface, enzymes can degrade the simplest external molecules to prevent them from penetrating the skin barrier. How convenient! The problem is that the number and distribution of these enzymes are not the same for everyone^3,13. This variability seems to be one of the clues to why some of us are more likely to develop allergies¹⁴.

Another clue lies in the ability of our white blood cells to control skin inflammation. These control white blood cells are not there to fight the enemy, but rather to calm things down. Their goal is to ensure that the body does not overreact and to minimize skin damage. An insufficient number of these white blood cells may promote sensitization and worsen the symptoms. However, stress, nutritional deficiencies, viruses, certain diseases, or age could also contribute to a decline in the number of these white blood cells¹⁵.

Where are these allergens hiding in our cosmetics?

Along with preservatives, they are the most common cause of skin allergies¹⁶. Fragrances are in fact a cocktail of dozens, or even hundreds of different molecules¹⁷. They can be synthetic or of natural origin, and are used in all types of cosmetics such as moisturizers, soaps, deodorants, masks, etc. Many of these substances are listed under the vague label of “fragrance” or “perfume”^18,19. This does not make it easy to identify an allergy to one of these highly allergenic substances. Lyral wins the award as the top allergenic substance according to the Scientific Committee on Consumer Safety (SCCS) and has therefore been banned from use in cosmetics in the European Union since 2019²⁰. In the USA, its labeling as an allergen is not mandatory and there is no regulation prohibiting its use in cosmetics¹⁹. Linalool, geraniol, limonene, natural lichen extract and citral are also known to cause allergic reactions.

Used as a fragrance or due to a wide variety of other properties, many of them are highly allergenic, particularly lemongrass essential oil, jasmine absolute, and sandalwood oil¹⁴.

On one hand, preservatives are beneficial because they inhibit the growth of microorganisms that could be dangerous to our health. However, some of them are powerful allergens. This is the case, for example, with MIT (Methylisothiazolinone) and MCIT (Methylchloroisothiazolinone). Yet they are used in nearly 20% of shower gels and shampoos²¹! And what do we know about Quaternium-15? 7% to 10% of Americans are allergic to this substance^22,23. It has been banned in the European Union since 2019²⁴. Let’s not forget 2-Bromo-2-nitropropane-1,3-diol which is reported to cause allergies in almost 3% of the population according to American studies^22,23.

These compounds are used to absorb the sun’s harmful UV rays which can damage the skin. They are very important in preventing cell aging and the development of skin cancer. But there’s a catch! After exposure to sunlight, some of them can be allergenic. This phenomenon is known as photosensitivity. This is the case with avobenzone, homosalate as well as compounds in the benzophenone family, which are nevertheless widely used ingredients in sunscreen products²⁵. And that’s not all! When they are combined with vitamin A (aka retinol) found in some day creams, this phenomenon may be more pronounced²⁶.

When the good guys become villains.

Some compounds are not allergenic per se, but can degrade into allergenic molecules. This is the case with so-called “formaldehyde-releasing” preservatives such as benzylhemiformal, diazolidinyl urea, DMDM hydantoin, imidazolidinyl urea and methenamine^23,27. Their degradation into allergenic molecules is mainly dependent on the cosmetic formulation, acidity, exposure to sunlight and temperature²⁸. Fragrance substances are also subject to this phenomenon. The oxidation of limonene, through exposure to sunlight, caused contact allergy in 3% of subjects tested according to one study¹⁴. This compound is present in virtually all plant extracts: essential oils, perfumes, floral waters, etc²⁹. This poses a serious problem.

In practical terms, what can be done?

• Avoid exposure to contact allergens as much as possible. This will considerably limit sensitization of the immune system to these substances.
• Avoid fragrance substances, even if they are labeled as “natural” or “based on essential oils”. The fact that fragrances are labeled “natural” does not guarantee that they won’t trigger skin irritations or allergic reactions.
• Be particularly vigilant in cases of atopic eczema or chronic irritation, even if this condition has existed since childhood. These pathologies increase the risk of developing a sensitization to contact allergens. The onset of the allergy’s elicitation phase is still possible during adulthood.
• Avoid over-cleansing of the skin. Excessive use of soaps and skin stripping products like scrubs can alter the skin’s natural protective barrier. This can allow the enhanced penetration of allergens and facilitate sensitization to these compounds.
• Take care of your skin with appropriate emollient and moisturizing creams. This will help to maintain the skin’s protective function against external aggressors³⁰.
• When purchasing a product, it is not enough to check for terms such as “hypoallergenic formulation”, “dermatologist tested”, “safe for sensitive skin”, “fragrance-free” or “organic”. These claims do not guarantee the absence of allergens in the formulation¹⁹.
• If you develop a contact allergy, consult an allergist to identify the cause and prevent future skin reactions.

Authors: Zoé Kerlo, toxicologist, and Séverine Fernandez, allergist.