How can we determine if we are allergic to a cosmetic product?

Redness, itching, swelling, blisters... If you wake up one morning with these symptoms on your face or any other area where you have applied a cosmetic, you may be suffering from a contact allergy to a product. Cleanser, serum, moisturiser... It's not always easy to identify which cosmetic is the culprit as allergic reactions often take 12 to 48 hours to appear. Indeed, cosmetic allergy progresses in two phases:

1. The sensitisation phase.

   The sensitisation phase occurs during the initial contact between the allergenic substance and the skin. After penetrating the epidermis, the allergen present in the cosmetic forms a complex with natural proteins of the skin tissue. The lymphocytes, white blood cells of the immune system, then come into play. After presenting the allergen's antigen to the lymphocytes, they transport the complex throughout the body.

   Lymphocytes also exhibit an intriguing characteristic: their ability to form memory cells. After eliminating the allergen, a portion of the activated lymphocytes differentiate into memory cells. These entities then patrol the body, enabling a swift and robust immune response if the organism is exposed to the same antigen again. The sensitisation phase can last from a few days to a few weeks, without any visible symptoms of skin lesions.

2. The revelation phase.

   From the second application of the allergenic cosmetic, it is recognised by the immune system, through memory cells. The lymphocytes then release lymphokines, a specific class of cytokines that direct the immune system's response, causing itching, redness, and skin lesions. As mentioned earlier, the initial symptoms of the cosmetic allergic reaction occur several hours after exposure.

   After the responsible allergen is removed, allergic symptoms generally decrease within the week following exposure and completely disappear after about ten days. If the offending product is not identified and continues to be applied, the allergic reaction persists and can extend to large body areas, and in some severe cases, it may even become infected.

True allergy or simple irritation: how to distinguish between them?

From a biological perspective, cosmetic allergy should be differentiated from an irritative reaction. The former largely depends on each individual's unique allergic profile, while the latter is more commonly encountered by sensitive skin types or manifests when the skin is weakened. Moreover, a cosmetic allergy involves prior sensitisation with activation of the immune system , whereas an irritative reaction is immediate. As soon as an irritating substance is applied to the skin, tingling and itching are immediately felt and red patches appear. The irritative reaction is due to the direct contact of the product with the skin, without the immune system having been activated. It is therefore advisable to immediately rinse the skin to remove the cosmetic and halt the reaction.