What type of reaction should a barber watch for when applying hair products?

When a barber applies hair products, it is crucial to monitor for allergic reactions such as rash or swelling. These reactions can occur when a client is sensitive or allergic to one or more ingredients in the hair products. Symptoms of allergies can manifest quickly and may include redness, itching, swelling, or rashes on the scalp or skin, which can indicate the need to discontinue use and seek medical advice.

In contrast, immediate discoloration may occur as a result of certain hair color treatments, but it does not typically indicate a negative bodily reaction, whereas delayed hair growth is more of a long-term concern unrelated to the immediate effects of hair product application. Breakage of hair is also an important consideration but is usually seen as a result of over-processing or mechanical damage rather than an immediate bodily reaction. Therefore, while potential issues such as breakage and discoloration are important to note, the immediate health and safety of the client makes monitoring for allergic reactions the most critical factor when applying hair products.