Novel Measurement of Invisible Photodamage in the Skin via the Detection of Biophoton, an Ultraweak Photon Emitted from the Body

Skin is exposed to various kinds of stress in daily life and continuously incurs invisible forms of damage. Ultraviolet (UV) light, a leading cause of damage, not only induces a sunburn/suntan response in skin, but also accelerates symptoms of skin aging such as spots, wrinkles, and sagging via the process of photoaging. While UV damage can be detected by a conventional method of measuring erythema the day after UV irradiation, this method fails to sufficiently discern forms of damage hidden from the human eye. Kao has thus been exploring an epochal method to measure hidden skin damage as a tool for reinforcing sun protection in order to realize the essential goal of maintaining beautiful and healthy skin throughout life.

UV exposure generates a reactive oxygen species (ROS) that leads to the oxidation of biological components in the skin. Considering the significant role of lipid peroxidation in UV-induced skin damage, Kao researchers wondered if the level of ROS-induced lipid peroxidation could be detected. To achieve this, Kao has focused on biophoton, an ultraweak photon emitted from the body. Although biophotons are known to be generated from both ROS and some types of oxidized lipids (Figure 2), it has not yet become possible to refine those lipid peroxides that contribute most to skin damage.

Here Kao has examined detailed changes in biophotons after UV exposure using an advanced photon detector. Biophoton signals can be observed up to a few minutes after UV exposure, but most signals disappear within the first minute. Kao researchers were surprised to determine that the biophotons related to lipid peroxides were emitted from 1 to 3 minutes after UV exposure (shown in the yellow rectangle in Figure 3). Apparently, this long-lasting biophoton emission strongly correlates with changes in skin redness read by a conventional color meter (Figure 4).

Further research has also revealed that substantial biophoton signals are produced in a UV dose-dependent manner even though there is no detectable change in skin color (redness) at lower energy levels. This finding makes it possible to perform highly sensitive detection of invisible skin damage by measuring the long-lasting biophotons emitted from 1 to 3 minutes after UV irradiation (Figure 1).

The accumulation of UV-induced skin damage is well known to accelerate symptoms of photoaging such as pigment spots, wrinkles, and sagging of the skin. By helping us understand invisible damage in the skin, this newly developed method can lead to the development of technologies to protect against even slight UV-induced damages that have considerable impact on photoaging.