Cleanliness may be next to godliness, but that doesn't mean it's always eco-friendly.

Take exfoliants. Among the most popular skin-care products, they come in two varieties: chemical and physical.

Chemical exfoliants use, well, chemicals to dissolve the dead cells sitting on the surface of the skin. Physical exfoliants use abrasives to scrape away those cells. Neither method is without drawbacks.

"There are no required studies for personal-care products," says Stacy Malkan, author of "Not Just a Pretty Face: The Ugly Side of the Beauty Industry."

"There are no safety systems in place, no governing bodies overseeing the industry."

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Most chemical peels use natural ingredients to eat away the top, dead layer of skin, leaving newer, healthier skin on the surface.

As such, they have few adverse effects on the environment — but they do leave people who use them at higher risk for sunburn and associated skin cancers.

"Because of this, many come with sunscreen built in," says Kristan Markey, a research analyst with the Environmental Working Group. "Many of the common petroleum-based sunscreens have bad environmental effects."

"But the bigger problem is from parabens and phthalates," Markey adds. "Parabens are widely used as preservatives and have all sorts of neurotoxicity concerns, while phthalates are solvents that can disrupt reproduction."

Among physical exfoliants, the most widely favored are aluminum oxide crystals, used in a spa treatment called microdermabrasion.

They're harmless to humans, but when you're done washing your face, those same crystals go down the drain, into the sewers and out into the ocean, where they do no good.

The EPA flatly states that any form of aluminum is "highly toxic to many species of aquatic organisms."

In fish, the metal has been linked to birth defects, increased mortality and a host of other complications.

Daniel Watts, an environmental scientist at the New Jersey Institute of Technology, has found that very high concentrations of aluminum oxide nanoparticles stunt root growth in plants.

Aluminum generally is regarded as safe for humans to ingest in low quantities, except for those on kidney dialysis, although there may be a link to Alzheimer's disease.

Markey points out that the real problem may be the process that manufactures nanoparticles.

"Exfoliants require really tiny particles," she says. "The manufacturing process releases those into the atmosphere, where they can scar lung tissue and have led to tumors in animal models."

Another danger comes from polyethylene microspheres, tiny plastic beads that have replaced natural abrasives such as apricot pits or pumice in many home and spa facial scrubs.

Polyethylene is what scientists describe as a long molecule, meaning it's hard to break down. And as with aluminum oxide, when you're done cleaning up, those polyethylene beads get washed into the ocean, where almost nothing can break them down.

There's also increasing proof that zooplankton, among the lowest links in oceanic food chains, are ingesting polyethylene alongside their normal diets.

"By itself and at this size, polyethylene is harmless to zooplankton," says Tony Andrady, senior research scientist at North Carolina's Research Triangle Institute and editor of the definitive "Plastics in the Environment."

"The problem is [that] polyethylene is also really good at absorbing and concentrating toxins — and those aren't harmless."

Among the toxins Andrady mentions are long-time ecological nightmares such as PCBs and DDT.

PCBs, which were completely banned in the 1970s, and DDT, which was mostly banned, keep showing up at alarming levels at all levels of oceanic food chains.

But there are organic alternatives. Avalon Natural Products has replaced chemical exfoliants with botanical alternatives such as pineapple enzyme and lavender enzyme, both for the same effect.

Old-school physical exfoliants such as apricot seeds and corn cob have begun making a comeback, as well. (Avalon uses certification programs to make sure its corn cob is of the non-genetically modified variety.) Eminence Organic Skin Care is experimenting with everything from poppy seeds to crushed almonds.

While all of these ingredients are eco-friendly, none can quite match the bamboo that shows up as the abrasive in Zia Natural Skincare's Bamboo Exfoliant.

Not only is bamboo the world's fastest-growing plant, but proper harvesting techniques do not kill the plant, so topsoil is held in place, further preventing soil erosion.

According to the San Francisco-based market research group SPINS, the natural products portion of the body care business is booming, showing increased growth every year since 2001 — good news for our skin and our planet.