Identify one common hair color product that requires a patch test.

Hair dyes or colorants are a common hair color product that require a patch test due to their potential to cause allergic reactions. A patch test helps determine an individual's sensitivity to the ingredients in the dye by applying a small amount of the product to a discreet area of skin, usually behind the ear or on the inner arm, and observing for any adverse reactions over a period of time. This precaution is important because some hair dyes contain strong chemicals, such as ammonia or peroxide, which can cause irritation or allergic responses in some users.

Shampoos, conditioners, and hair moisturizers typically do not contain the same level of harsh chemicals found in dyes and are generally considered safer for routine use, thus they do not require the same testing procedures. Testing for these products is usually not necessary unless the individual has specific known sensitivities or allergies to ingredients used in the formulation.