Final answer:
Before using a depilatory product, an allergy test, such as a patch test, should be performed on the skin to prevent adverse reactions.
Step-by-step explanation:
Prior to using a depilatory product, it is recommended to perform a patch test on the skin. This is essential to ensure that the individual does not have a type I hypersensitivity or an allergic reaction to the ingredients in the product. A patch test involves applying a small amount of the product to a discreet area of the skin, often behind the ear or on the inner forearm, and waiting to see if there is any adverse reaction, such as redness, itching, or swelling.
If an allergic reaction occurs, indicated by a wheal and flare response, the product should not be used. This precautionary step helps identify any potential allergens, as skin testing helps allergists diagnose allergies in a similar manner. Therefore, the correct answer to the question is A: An allergy test.