Call it a new spin on the phrase "skin deep".

In our society, youth is king. There is an entire industry aimed at making people look younger - everything from creams to hairpieces to surgery can be obtained if a person really wants to stop the biological clock. However, research indicates that, despite humans' best efforts, nature can still give them away. In a study published in the latest issue of Biomedical Optics Express, scientists were able to use lasers to determine a person's age from their most shallow layer - their skin.

The technique, called harmonic generation microscopy or HGM, was used on 52 subjects who were between the ages of 19 and 79 years old. The researchers focused on the subjects' inner forearm, a part of the body that is largely not exposed to sun damage. Researchers wanted to examine a part of the body that would not have been affected to sun damage because damage from UV-rays can accelerate natural aging. The scientists used a brief burst of infrared laser light into the skin, which penetrated 300 millionths of a meter, at about the layer where the upper layer of skin, the epidermis, meets with the lower layer, the dermis.

Harmonic generation microscopy has previously been used to study developing embryos. It uses a concentrated group of photons that generate vibrations as they interact with an object. Using that system, researchers were able to generate 3-D maps of the tissue that makes up skin cells. They found that natural aging increases the sizes of the cells and nuclei of basal keratinocytes, the most common type of cells on the outer layer of skin. The other type of cells, granular cells, did not have this same change though.

Researchers hope to create a skin index that can show whether the cells of some populations of people age more quickly than other populations or even see whether anti-aging tools actually slow down the aging process.

"Of course," study authors Chi-Kuang Sun and Yi-Hua Liao joke, "you could set an HGM scanner at the entrance to a bar, so you can know whether a person is over 21 years old and permitted for entry."