How do you perform a patch test?

The correct choice is to perform a patch test on the inside of the forearm for sensitivity. This area is preferred because it typically has skin that is representative of the rest of the body, yet is easy to observe for any adverse reactions. Performing a patch test here allows for a controlled environment where the reaction can be monitored, minimizing the potential for discomfort since it is a less exposed area.

Using the forearm also allows for enough space to apply the product and observe any immediate or delayed reactions without the risk of affecting cosmetics or other products that may be in use on areas like the face or back. It's important to ensure that the testing method is done on skin that is sensitive yet also protected from extensive exposure to sun or irritation, which the forearm fulfills.

In contrast, testing on the shoulder or the back may not provide a clear view of potential reactions, especially if the area is covered or if clothing irritates the test site. Testing directly on the face can be risky, especially for individuals who may have sensitive skin, because a reaction could involve significant discomfort or an unsightly response that could be more difficult to treat or manage initially.