Beauty is only skin deep, and now scientists can use a laser microscopy technique to gauge a person’s true age from his/her most shallow layer — the skin. The method could provide a standardized way to measure the extent of skin damage and the effectiveness of anti-aging skin products. The technique, harmonic generation microscopy (HGM), was developed by researchers at National Taiwan University and used to peer harmlessly beneath the skin surface of 52 subjects between the ages of 19 and 79 to measure natural age-related changes in the sizes of skin cells. The researchers focused a brief burst of infrared laser light on the subjects’ inner forearm, a part of the body generally protected from sun damage. The beam 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. This series of harmonic-generation-microscopy images shows the skin cells of a 24-year-old subject at increasing depths, ranging from the outermost layer of skin (a) to approximately 300 millionths of a meter deep (f). The magenta areas, generated from third harmonics, show skin cells and their nuclei. The green areas, generated from second harmonics, show fibers made of the protein collagen. Images courtesy of Biomedical Optics Express. HGM, a method previously used to study developing embryos, uses a concentrated beam of photons to generate vibrations as they interact with an object. In their study, the researchers scanned for reflected second- and third-harmonic photons, generating 3-D maps of the tissue that makes up skin cells. They discovered that natural aging increases the sizes of cells and the nuclei of basal keratinocytes, the most common type of cells on the outer layer of skin. The other type of cells — granular — did not show a similar pattern. “No one has ever seen through a person’s skin to determine his or her age,” said professor Chi-Kuang Sun, chief director of the university’s Molecular Imaging Center. “Our finding serves as a potential index for skin age.” These images of basal keratinocytes, the most common cells in the outermost layer of skin, were taken of the forearms of a 24-year-old (a), a 47-year-old (b), a 59-year-old (c) and a 69-year-old (d). Compared with the skin cells of the youngest volunteers, the skin cells in older subjects were larger, more irregular in shape and showed spaces between cells, as indicated by the white arrows in images b-d. A skin index could enable doctors to see whether the cells of some populations of people age more quickly than others, or even see whether anti-aging tools actually slow down the aging process. “Of course, 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,” researcher and dermatologist Yi-Hua Liao joked. The findings were detailed in Biomedical Optics Express.