First stop: the office of dermatologist Dennis Gross, MD, where his luminous assistant, Magda, applies an exfoliating alpha hydroxy acid peel to my face and neck. When the (unlined) doctor enters the room, he explains that the change in pH level in the skin created by just one acid peel can generate collagen, the key to skin that ages well. "Collagen is the skin's structural fiber," he says. "As we get older, it breaks down, creating lines and large pores." What speeds up the degeneration? Sun exposure. "The absolute worst thing you can do is sit in the sun," he says. Sun exposure causes up to 90 percent of wrinkles, dark spots, and sagging. "It can take 10 years to see the effects, so people don't make the connection between a golden tan now and visible damage later," he says. "But by wearing broad-spectrum sunscreen and using topical treatments with as many proven collagen-producing ingredients as possible—including retinol and antioxidants, such as green tea extract and vitamin C—even a person who spent years recklessly sunbathing can make a turnaround."