WASHINGTON (Reuters) – U.S. health regulators said consumer products that use nanotechnology may have unknown effects on the human body, and advised food and cosmetic companies on Friday to further study the safety of these tiny particles.

Nanotechnology involves designing and manufacturing materials on the scale of one-billionth of a meter – so small it cannot be seen with a regular light microscope.

It is used in hundreds of products in areas ranging from stain-resistant clothing and cosmetics to food additives, but the health effects of nanoparticles are still poorly understood.

Nanoparticles may be able to penetrate the skin, or move between organs, and scientists do not always understand what effect this will have.

The U.S. Food and Drug Administration issued two draft guidelines on Friday calling for more studies, suggesting the FDA is early in its review of the nanotech world and for now is putting much of the onus on companies to be responsible for product safety.

“Understanding nanotechnology remains a top FDA priority,” FDA Commissioner Margaret Hamburg said in a statement. “FDA is strengthening the scientific tools and methods for evaluating food products, cosmetics, drugs and medical devices.”

The FDA advised companies that use nanotech in food additives or food packaging to consult with the agency and show that the changes are safe before selling their products.

“The consequences (to consumers and to the food industry) of broadly distributing a food substance that is later recognized to present a safety concern have the potential to be significant,” the draft guide says.

Makers of U.S. food additives and ingredients must prove that their ingredients are “generally recognized as safe” in order to legally sell them.

The FDA said nanotechnology does not automatically fall into this category, meaning companies would have to show additional safety data before approval.

For cosmetics, the FDA said companies should also do additional testing of products that, for example, use nanotechnology to create smoother-feeling moisturizers or lipstick.

(Reporting by Anna Yukhananov; Editing by Tim Dobbyn)