What is a common symptom of an allergic reaction to a cosmetic product?

A common symptom of an allergic reaction to a cosmetic product is redness and swelling. When the immune system identifies a substance in a cosmetic as harmful, it can respond by triggering inflammation. This manifests as redness, which is due to increased blood flow to the affected area, along with swelling caused by the accumulation of fluids and immune cells. These symptoms are typical of an inflammatory response, as the body attempts to protect itself from what it perceives as an allergen.

Dryness could occur in some skin conditions or reactions, but it is not a definitive sign of an allergic reaction. Excessive oiliness might not be directly related to allergic reactions; rather, it could be a result of other skin conditions or factors. Increased sensitivity to light may also occur due to various skin conditions or reactions but is not a primary symptom of an allergic reaction to cosmetics. Therefore, redness and swelling are the hallmark signs indicating an allergic response to cosmetic products.