Use them: Nightly to prevent breakouts.
How they work: Retinoids, which include over-the-counter retinol and prescription-strength Retin-A, reduce acne by altering the oil chemistry on the skin. “They help stop dense sebum from getting stuck within the pores,” says Gross. Without oil deposits, bacteria can’t grow and cause blemishes. Try SkinCeuticals Retinol 1.0 ($63, skinstore.com).
Good to know: Since retinoids can make skin sensitive to the sun, doctors recommend using them at night (and being diligent about wearing sunscreen during the day). To avoid irritation, apply every other evening to start, gradually working up to nightly use. Bonus benefit: Retinoids have been shown to increase collagen production and plump fine lines, making them a good choice if you’re dealing with acne and wrinkles.