Ask a derm
Q: What's the difference between day creams and night creams, and do you need to use both?

A: "Night creams tend to be richer and often contain vitamin A, which can cause photosensitivity during the day," says Dr. Lisa Kellett of DLK On Avenue. "Conversely, day creams contain an SPF, which you don't need at night. Technically speaking, you don't need to use different creams for day and night unless you choose a product containing vitamin A. And if you have dry or mature skin, switching to an ultra-rich cream at night will give you the skin-care benefits you need without leaving your skin greasy during the day."

L'Oréal Paris Dermo-Expertise Advanced Revitalift Night ($29).