What are the signs of an allergic reaction to hair dye?

An allergic reaction to hair dye typically manifests through symptoms such as rash, itching, or swelling. This occurs due to the body's immune response to certain chemicals present in the dye, particularly those such as paraphenylenediamine (PPD). When a person is allergic to these substances, exposure can lead to inflammation in the skin, which presents as redness, swelling, and irritation. These symptoms are localized to areas where the dye has been applied, such as the scalp, neck, or ears.

While other options may represent hair or scalp conditions, they do not directly indicate an allergic reaction. For instance, dryness and split ends are often related to the health of the hair itself and may be the result of over-processing or lack of moisture, rather than an immune response. Dandruff or flakiness can be caused by various scalp issues like dry skin or fungal infections, and hair loss might occur from numerous factors including stress or hormonal changes rather than an immediate allergic reaction. Thus, rash, itching, or swelling is a distinctive sign of an allergic reaction, making that option the correct choice.