Search online for DIY sunscreen recipes and you'll find hundreds of thousands of results. People say they're opting for homemade sunscreen for several reasons. Many want to know exactly what they're applying to their skin. Others want to make sure to skip "toxic" chemicals and go a more natural route. And many just want to save money. But homemade sunblock doesn't necessarily fulfill those promises.

Sunscreens are regulated by the U.S. Food and Drug Administration (FDA) to make sure the active ingredients are safe and the SPF and broad spectrum coverage is proven. When you whip up your own concoction, you may know what ingredients you're applying, but you have no clue about protection.

"You cannot possibly make your own sunscreen because it’s hard enough for companies to make sunscreens that are accurate in SPF as is. Thus that is a bad idea," New York-based board-certified dermatologist Debra Jaliman M.D. tells MNN.

"A myth about sunscreen I frequently hear is that the chemicals in sunscreens are dangerous. When was the last time you read an article about someone dying from the chemicals in sunscreens? We have certainly read many articles about people dying from malignant melanoma and one person dies every hour from malignant melanoma in the United States."

When you apply DIY sunscreen, you have no idea if you — or your children — will be protected until you take the risk of heading out into the sun and find out if you burn or not.

And just one bad sunburn during childhood or adolescence can nearly double the risk of developing skin cancer, according to the American Academy of Dermatology. Having five bad sunburns between 15 and 20 raises the risk of melanoma by a whopping 80 percent.

“The long and short of it is that it is better to trust the pros than try to make this stuff at home," Sonya Lunder, senior analyst at Environmental Working Group, tells MNN. “Formulating sunscreens is an art and a science.”

You don't know what you're getting

Woman with umbrella If you worry about chemicals in sunscreen, you can buy clothing and sun umbrellas with SPF in them. (Photo: Alexander Chaikin/Shutterstock)

Many of the DIY sunscreen recipes involve a mixture of zinc oxide, shea butter and oils. Paste zinc oxide can be an effective sunblock and is often used by lifeguards, says Rebecca Baxt, M.D., a board certified dermatologist who practices in Paramus, New Jersey,

"Plain zinc oxide is the best sunblock since it's a physical barrier and not much gets through it. It's a white paste so people don't like to use it much," she says. "It's not cosmetically pleasing."

But the zinc and titanium suggested in most DIY sunscreen recipes is generally in power form.

Lunder especially cautions people against buying nano forms of zinc and titanium powder. “The particles are much more absorbed by the lungs and nasal passages — which is why we don’t recommend people use powder or spray sunscreens.”

Other DIY recipes just include a mix of essential oils. In those cases, that might leave you with no sun protection at all. You could also have an unpleasant response to ingredients.

"Making your own sunblock is unproven and untested so it's very easy to get a sunburn or allergic reaction and rash," Baxt says.

If you're worried about having an all-natural, chemical-free solution, there's a much safer, more effective alternative, she suggests.

"The best non-chemical sunblock is clothing, hat, umbrellas, and you can get those with SPF in them!"

And if you're trying to save money, Consumer Reports says doing it yourself isn't always the most economical way. On of the "best buys" on the organization's recent sunscreen rankings included one that was only 79 cents per ounce, which is likely cheaper than the ingredients you'd purchase to make sunscreen at home.

Editor's note: This story was originally written in July 2009 and has been updated.

Mary Jo DiLonardo writes about everything from health to parenting — and anything that helps explain why her dog does what he does.