What is one common sign of an allergic reaction to a skincare product?

A common sign of an allergic reaction to a skincare product is the presence of redness, swelling, or itching. Allergic reactions occur when the immune system identifies a substance in the product as harmful, prompting a response that often manifests as inflammation. This inflammation causes the skin to become red and swollen as blood vessels dilate and more blood flows to the area, while itching results from the irritation of nerve endings in the skin.

In contrast, nausea, dry patches, and increased oiliness are not typically associated with allergic reactions. Nausea may indicate systemic reactions rather than localized skin responses. Dry patches can result from various factors, such as dehydration or a lack of moisture, and increased oiliness may be due to other skin conditions or product formulations, but these do not indicate an allergic response to the ingredients in the product. Therefore, the hallmark signs of allergy-related skin reactions remain the redness, swelling, and itching.