Choosing skin care products can be overwhelming. There are so many ingredients and so many claims of benefits.

But there is one ingredient that has stayed the course since its introduction in the 1960s. Retin-A is a form of vitamin A used to rejuvenate skin and, in some cases, treat skin spots that may be precancerous. 

“Retin-A is a great product,” says dermatologist Anisha Patel, M.D. “The active ingredient is tretinoin...