Scientists are warning that tiny particles - nanoparticles - are so small that they can be absorbed through the skin.
Nanoparticles are found in electronics, food containers, sunscreens and a variety of applications, and scientists from University of Rochester Medical Center, say they are able to breech the human body's most personal protective barrier, the skin.
Dr. Lisa DeLouise says the particles under scrutiny are almost unfathomably tiny, measuring less than one five-thousandth the width of a human hair.
Dr. DeLouise has found that nanoparticles can pass through the skin of a living organism, providing the strongest evidence yet that some nanoparticles are so small that they can actually seep through skin, especially when the skin has been damaged.
This was discovered in experiments using specially bred mice commonly used as a model to study the damaging effects of sunlight - it was found that the particles accumulated around the hair follicles and in tiny skin folds.
DeLouise, an assistant professor of Dermatology and Biomedical Engineering and an expert on the properties of nanoparticles says the health implications of nanoparticles in the body are uncertain.
Other scientists have also found that nanoparticles can accumulate in the lymph system, the liver, the nervous system and in other areas of the body.
Dr DeLouise says the study did not directly address the safety of nanoparticles in any way but was conducted to see if nanoparticles could pass through the skin and it was found that under certain conditions they can.
DeLouise's work is part of a broad field known as nanomedicine that is a strategic area at the University of Rochester Medical Center, and includes research looking at the properties of nanoparticles, as well as possibilities such as new forms of drug delivery and nano-sensors that can immediately identify microbes and other threats to our health.
Nanoparticles are becoming widely used in the manufacture of consumer products and are also the subject of a great deal of research; some of the particles are so small, less than 10 nanometers wide (a nanometer is one-millionth of a millimeter), that they are nearly as small as the natural gaps between some skin cells.
The Rochester team studied the penetration of nanoparticles known as quantum dots that fluoresce under some conditions, making them easier to see and track compared to other nanoparticles - they looked at the distribution of quantum dots in mice whose skin had been exposed to about the same amount of ultraviolet light as might cause a slight sunburn on a person.
The team found that while the nanoparticles were able to breech the skin of all the mice, the particles passed more quickly through skin that had been damaged by ultraviolet light.
Future research by Dr. DeLouise will involve titanium dioxide and zinc oxide, two materials that are widely used in sunscreens and other cosmetic products to help block the damaging effects of ultraviolet light.
In recent years the size of the metal oxide particles used in many consumer products has become smaller and smaller, so that many now are nanoparticles.
DeLouise says the materials are often completely transparent when applied to skin - a transparent lip gloss that protects against UV light or a see-through sunscreen may contain nanoparticles.
DeLouise says many people apply sunscreens after their skin has been damaged by sunlight and while older sunscreens have larger particles that reflect visible light, many newer sunscreens contain nanoparticles that are one thousand times smaller, that do not reflect visible light.
The report is published in the September issue of the journal Nano Letters.