Which of the following can be a sign of an allergic reaction during a patch test?

A patch test is an important procedure conducted before applying hair color products, particularly those containing potential allergens. An allergic reaction can manifest in several ways, and one key indicator is the presence of redness, swelling, or a rash at the site of the test. These symptoms suggest that the body is responding negatively to the ingredients in the hair color, which is critical for all hair professionals to recognize.

Redness indicates irritation or inflammation, swelling shows that the area is reacting, and a rash signifies that the skin has developed an adverse response. These signs are not only important for the client's safety but are also crucial for preventing potential severe allergic reactions, which can happen during the actual hair coloring process.

In contrast, improved hair texture, increased shine, or faster color processing do not relate to allergic reactions. These aspects may indicate positive outcomes from the hair treatment but do not provide any information regarding a client's safety or well-being in relation to allergies.