What It’s Meant to Do: A toner purportedly eliminates oil, tightens pores, and gets the skin ready to absorb active ingredients in other products.

So Who Needs It? Only people with extremely oily skin, says Ranella Hirsch, M.D., vice president of the American Society of Cosmetic Dermatology and Aesthetic Surgery. And that’s only if you’re not already controlling oil in another way, like with a salicylic acid–based cleanser or an oil-absorbing lotion. (Incidentally, “there’s no truth to the theory that toners prep the skin or help other products penetrate better,” says David E. Bank, M.D., director of the Center for Dermatology, Cosmetic and Laser Surgery, in Mount Kisco, New York.)

RS Pick: Lierac Toner, $25, www.beauty.com.

Who Can Skip It: Women with normal, dry, or sensitive complexions — that is, almost everyone. Toners often overdry these types of skin, triggering the sebaceous glands to pump out more oil in an effort to prevent dehydration. The result: rebound greasiness and more breakouts.