Overloading On Products
"I ask patients to walk me through their routine, and they bring in shopping bags full of products," says New York City dermatologist Patricia Wexler. "They add things without checking to see whether they're duplicating ingredients or realizing that some aren't compatible." Sometimes, active ingredients cancel one another out—Other times, they double up and cause irritation or skin damage. "Negative interactions are most likely to happen if someone is treating different problems at the same time, such as sun-damaged skin and adult acne, and the ingredients are either too harsh together or incompatible," says Baumann. The biggest culprits: retinol, glycolic acid (aka AHA's), vitamin C, and benzoyl peroxide—avoid layering them, or at least try to use them at different times of day.