Taiwanese researchers have used a specialised microscope to peer harmlessly beneath the skin’s surface to measure natural age-related changes in the sizes of skin cells. The results, which are published today in the article “Determination of chronological aging parameters in epidermal keratinocytes by in vivo harmonic generation microscopy” in the Optical Society’s (OSA) open-access journal Biomedical Optics Express, can be used to study the general phenomenon of skin aging and may help provide an index for measuring the effectiveness of “anti-aging” skin products.
In the study, Chi-Kuang Sun, a distinguished professor at National Taiwan University and chief director of the university’s Molecular Imaging Centre, along with medical researcher and dermatologist Yi-Hua Liao and colleagues, evaluated 52 subjects ranging in age from 19 to 79 years old. The researchers focused a brief burst of infrared (IR) laser light into the skin of the subjects’ inner forearms, an area that is generally protected from sun damage, which accelerates natural aging. The beam penetrated to a depth of about 300 millionths of a metre, or approximately where the epidermis (the upper layer of skin) and the dermis (the lower layer) meet.
Figure 1: 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. Credit: Biomedical Optics Express.
The researchers used a technique known as harmonic generation microscopy (HGM), which has previously been used to study developing embryos. In the procedure, a concentrated beam of photons is sent into a material. The photons naturally oscillate at a particular frequency and as they interact with the material, they generate “harmonics” (i.e., vibrations that are multiples of the original frequency), which are characteristic of the material’s structure and properties. For example, the second harmonic is twice the original frequency and the third harmonic is three times the original frequency. In an imaging system, harmonics can reveal different structures at high resolution. In their study, the team scanned for reflected second and third harmonic photons and from those measurements produced a high-resolution three-dimensional (3D) map of the tissue that revealed structures within the skin cells.
Figure 2: This shows images of basal keratinocytes, the most common cells in the outermost layer of skin. The images 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 to 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. Credit: Biomedical Optics Express.
Natural aging, the scanning showed, caused a significant increase in the overall size of cells known as basal keratinocytes, which are the most common cells in the outermost layer of skin, as well as in the sizes of their nuclei. However, other types of skin cells, known as granular cells, did not show a similar pattern. Thus, says Sun, the relative changes in the two types of cells can serve as an index for scoring natural skin aging, which is the aging of skin caused by programmed developmental or genetic factors.
“No one has ever seen through a person’s skin to determine his or her age from their skin,” says Sun. “Our finding serves as a potential index for skin age.”
A skin age index would provide a standardised, quantitative scale that could be used to rate the true age of the skin, from young (less age-related damage) to old (more age-related damage). The scale could give doctors another tool to monitor the overall health of skin by investigating whether the skin of certain individuals or populations ages more quickly or more slowly than average; tracking the aging of an individual’s skin over time; or testing how effective anti-aging treatments are at slowing the rate of skin aging.
Written by Jane Morrill, Special Projects Editor, Novus Light Technologies Today