June 5, 2024
In today's post we are going to delve into a fascinating but sometimes worrying topic : why can perfumes and essential oils cause skin allergies?
Perfumes and essential oils are a fundamental part of our beauty and wellness routines, yet they can be a source of discomfort for those with sensitive skin or who are prone to allergies. Understanding the biology and chemistry behind these reactions can help us make more informed decisions about the products we use or formulate.
Before we get into the subject, we need to understand what a skin allergy is. Basically, a skin allergy is an overreaction of the skin's immune system to a substance that is generally harmless to most people.
The skin is our largest organ and acts as a protective barrier against the outside world. Within this barrier, we have cells of the immune system, such as keratinocytes (which in addition to the structural function have immunological function by early detection of "intruders"), mast cells and Langerhans cells, which are always on guard. These cells are like the security guards of a building, always ready to detect and fight any "intruder" that may pose a threat.
We usually refer to substances that can trigger an allergic reaction as haptens. When the hapten comes into contact with the immune system of a sensitized person, a reaction is triggered.
When the skin comes into contact with a hapten, these immune cells spring into action. They release a series of chemical signals that attract more immune system cells to the site of contact, triggering inflammation and other allergy symptoms.
This reaction can manifest as redness, itching, swelling, and in more severe cases, blisters. If you want to know more visit our previous Blog entry.
Perfumes and essential oils are complex mixtures of multiple chemical compounds, of natural or synthetic origin. Perfumes can contain dozens, if not hundreds, of different ingredients, from flower essences to synthetic compounds designed to mimic natural odors. Essential oils, while natural, also contain a variety of chemical compounds that can be potent. For example, chamomile essential oil contains more than 200 known substances.
These substances are usually very small and volatile molecules, as they can be perceived by the sense of smell. But this small size makes them easy to penetrate into the deep layers of the skin.
These substances include terpenes and other small molecules with aromatic rings.
Terpenes are natural chemical compounds present in many plants, including essential oils and perfumes. These compounds are responsible for the characteristic aromas of many plants, such as the smell of lavender, pine and citrus.
Chemically, they are made up of isoprene units (C5H8), and can be classified according to the number of these units they contain: monoterpenes (C10H16), sesquiterpenes (C15H24), diterpenes (C20H32), and so on. These compounds are the main components of essential oils and have a wide variety of structures and functions in plants.
The most common terpenes found in perfumes and essential oils include limonene, linalool, geraniol and eugenol.
Let's look at these molecules in a little more detail:
Oxidation: As mentioned above, terpenes are volatile and, when exposed to air, can oxidize. Oxidation is a chemical process in which terpenes react with oxygen in the air, forming reactive oxygen compounds such as hydroperoxides. These oxidation products are generally more allergenic than the original terpenes.
Adduct formation: Oxidation products can react with proteins in the skin, forming complexes known as adducts. These adducts can be recognized by the immune system as foreign substances, triggering an allergic response.
Recognition by the immune system: The adducts formed activate immune cells in the skin, initiating a cascade of chemical reactions that lead to inflammation and other allergy symptoms.
For an allergy to occur, the body must first become sensitized to the allergen. This does not usually happen on first contact. Sensitization is a process in which the immune system "learns" to recognize the allergen as a threat.
During the first exposure, Langerhans cells in the skin capture the allergen and present it to T cells (a type of immune cell). The T cells become activated and begin to multiply, preparing the immune system for future exposure to the allergen.
On subsequent exposures, the "memory" T cells quickly recognize the allergen and trigger a faster and stronger inflammatory response, which manifests as an allergic reaction.
It is therefore important to differentiate between allergic reactions and primary irritation or repeated irritation reactions.
Often, products can cause contact dermatitis, but do not trigger an allergic reaction.
According to the Scientific Committee on Consumer Safety (SCCS) it has not been possible to establish a safe limit of use for products containing these substances, but notes that most consumers with contact allergy to fragrance ingredients can tolerate a general level of exposure of up to 0.8 μg/cm2 (0.01%). However, there is a more sensitive segment of the population that may react to exposure at these levels, this committee adds, so sticking to the threshold does not eliminate the need to inform consumers about the presence of these substances.
The European Cosmetics Regulation requires that allergens must be declared on product labeling when their concentration exceeds 0.001% of the total concentration in non-rinse-off products (such as body lotion, face creams, colognes or makeup) or 0.01% of the total concentration in rinse-off products (shower gels, shampoo, etc.).
Known allergenic substances are listed in Annex III of restricted substances. Until last year, the list was 26 allergenic substances, but in 2023 it was expanded to 81 substances considered allergenic.
The skin is an incredibly effective barrier, but it is not impenetrable. Chemical compounds, natural or synthetic, present in perfumes and essential oils can, in some people, trigger an immune response that results in a skin allergy.
So the next time you enjoy that delicious lavender scent, the fresh citrus perfume, or want to formulate a product with essential oils remember that the science behind these products is complex and we can't reduce it to a list of good and bad.
And if you need help, feel free to subscribe to our newsletter or contact MUTTULab.
To a beauty full of knowledge!
Find out more about Celia Campos, Technical Director and co-founder of MuttuLab, author of this article.
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