Which symptom indicates that a cosmetic product may have caused an adverse reaction?

Swelling and rashes are clear indicators of an adverse reaction to a cosmetic product. This response occurs when the skin becomes irritated or inflamed, often as a result of an allergic reaction, sensitivity to an ingredient, or an incompatibility with the product. Such symptoms suggest that the skin is reacting negatively, which can stem from chemical components, fragrances, or preservatives used in the formulation of the product.

In contrast, oily skin and acne breakouts can be common skin conditions that do not necessarily indicate a reaction to a product, as they can arise from various factors such as hormonal changes or lifestyle choices. An improved complexion would typically suggest a beneficial effect from a product rather than a harmful reaction. Therefore, the presence of swelling and rashes is the most significant indicator of a potential adverse reaction.