Name a common symptom of an allergic reaction to hair color.

A common symptom of an allergic reaction to hair color is itching or redness. When individuals are exposed to certain chemicals found in hair dye, especially those containing paraphenylenediamine (PPD), the body may respond with an inflammatory reaction. This results in noticeable itching, redness, swelling, or rashes on the scalp or other areas where the dye has come into contact with the skin. These symptoms indicate that the immune system is reacting negatively to the substances in the hair color.

While excessive dryness, hair loss, and an oily scalp can be related to hair treatments or products, they are not directly indicative of an allergic reaction. Excessive dryness can occur from chemical processes or environmental factors, hair loss may result from various conditions or stress, and an oily scalp is often related to the scalp's sebaceous glands producing excess oil. Thus, these options do not reflect the immediate immune response that characterizes an allergic reaction like itching or redness does.