05/22/2009 AT 04:40 PM EDT
She's got one of the most recognizable – and radiant – faces in the world. But years of sun worship caught up with Brooke Shields
when she got some sobering news from her doctor recently.
"I had a spot on my face. The doctor scraped it, and it turned out to be precancerous," Shields, 43, tells PEOPLE. "I was scared."
The Lipstick Jungle
actress had the spot removed and says she's doing "fine." But the cancer scare served as a wake-up call for a woman who "used to think it was the best thing in the world to be baking in the sun" and who, as a teen, would indulge in hot-weather rituals like "baby oil and tinfoil and lemon in your hair."
"All my girlfriends and I would go up on the roof in New York; we didn't have to be at the beach," says Shields, who stopped actively tanning a decade ago. "You think that because you're not in the sun anymore, it's all in the past. And then something like that crops up and you're made aware of how dangerous it really can be."
Shields, who has put on a brave face as her mother Teri struggles with dementia
, was all smiles at an L.A. event this week to launch Coppertone Nutrashield, which claims to protect from sun damage while promoting skin repair. She says she decided to become the face of the brand with two people in mind: Rowan, 6, and Grier, 3, her daughters with husband Chris Henchy.
"My kids are translucent," she says laughing. "They have red hair. They reflect! I thought, 'My God, I've got to get more vigilant about it.'"
Shields – lauded by friends for her devotion
to both her mother and daughters – admits that slathering the girls with sunscreen isn't an easy task.
"They're totally not fine with it. They fight me," she says. "They do the thing where while you're putting it on, they're backing up. I'll lock my legs around them ... They're really fair, and they've already had sunburn. It has to be every day."
For more on Brooke, including more details of her evolving relationship with her mother, pick up the new issue of PEOPLE, on newsstands now