Exploitation of long-lasting ultraweak photon emission to estimate skin photodamage after ultraviolet exposure

Skin lightness affects ultraviolet A-induced oxidative stress: Evaluation using ultraweak photon emission measurement

The human skin is usually exposed to ultraviolet A (UVA) in the sunlight and experiences oxidative stress associated with skin disorders and aging. Although oxidative stress caused by UVA exposure is assumed to be dependent on skin colour, few studies have demonstrated this dependency. We investigated the effects of skin colour on UVA-induced oxidative stress using ultraweak photon emission (UPE) generated from the skin during oxidation processes. The UPE intensities of skin samples were detected using a photomultiplier tube every second without any labelling. We irradiated skin tissue of different colours with UVA and measured UPE over time. UVA-induced UPE could be detected from immediately after irradiation to 2 h after irradiation, indicating persistent oxidative stress. Skin lightness (L*) positively correlates with UPE intensity. Lighter-coloured skin exhibited more UVA-induced UPE, indicating higher oxidative stress. Additionally, oxidative stress persisted significantly more in lighter skin compared with darker skin. Skin tissues exhibited pigment darkening after UVA irradiation. Our results suggest that skin lightness affects oxidative stress induced by UV irradiation. Our study demonstrated the relationship between skin lightness and UVA-induced oxidative stress for the first time and offers new photodermatological insights into the human skin.

The application and trend of ultra-weak photon emission in biology and medicine

Ultra-weak bioluminescence, also known as ultra-weak photon emission (UPE), is one of the functional characteristics of biological organisms, characterized by specialized, low-energy level luminescence. Researchers have extensively studied UPE for decades, and the mechanisms by which UPE is generated and its properties have been extensively investigated. However, there has been a gradual shift in research focus on UPE in recent years toward exploring its application value. To better understand the application and trend of UPE in biology and medicine, we have conducted a review of relevant articles in recent years. Among the several topics covered in this review is UPE research in biology and medicine (including traditional Chinese medicine), primarily focused on UPE as a promising non-invasive tool for diagnosis and oxidative metabolism monitoring as well as a potential tool for traditional Chinese medicine research.

Evaluation of subclinical chronic sun damage in the skin via the detection of long-lasting ultraweak photon emission

BACKGROUND

It is well known that solar radiation accelerates skin photoaging. To evaluate subclinical photodamage in the skin especially from the early phase of ultraviolet (UV)-induced damage, we have focused on ultraweak photon emission (UPE), also called biophotons. Our previous study reported that the amount of long-lasting UPE induced by UV, predominantly from lipid peroxidation, is a valuable indicator to assess cutaneous photodamage even at a suberythemal dose, although it was only applied to evaluate acute UV damage. The aim of this study was to further investigate whether long-lasting UPE could also be a useful marker to assess subclinical chronic sun damage in the course of skin photoaging.

MATERIALS AND METHODS

Forty-three Japanese females in their 20s were recruited and were divided into two groups according to their history of sun exposure based on a questionnaire (high- and low-sun-exposure groups). Several skin properties on the cheek and outer forearm were measured in addition to UV-induced UPE.

RESULTS

Among the skin properties measured, water content, average skin roughness, and the lateral packing of lipids in the stratum corneum were significantly deteriorated in the high-sun-exposure group as were changes in some skin photoaging scores such as pigmented spots and wrinkles. In addition, those skin properties were correlated with the UPE signals, suggesting the possible impact of oxidative stress on chronic skin damage.

CONCLUSION

Subtle oxidative stress detected by long-lasting UPE may contribute to subclinical cutaneous damage at the beginning phase of chronic sun exposure, which potentially enhances skin photoaging over a lifetime.