What is a patch test? Why is it recommended to do a patch test when using a topical product for the first time?

A skin patch test is a quick and easy method of determining whether a product may cause an allergic response. If it's your first time using a topical product or if you have a history of sensitive skin, it can be a good idea to do a self-administered patch test. 

First, apply a small amount of the product to your skin and leave it on for at least a full day. Monitor for any possible reactions such as redness, itchiness, or discomfort. A reaction likely indicates an allergy to the product, in which case it should be washed off immediately and use should be discontinued.