Highlighting nuances of blue light phototherapy: Mechanisms and safety considerations

Abstract

The efficacy of blue light therapy in dermatology relies on numerous clinical studies. The safety remains a topic of controversy, where potentially deleterious effects were derived from in vitro rather than in vivo experiments. The objectives of this work were (1) to highlight the nuances behind “colors” of blue light, light propagation in tissue and the plurality of modes of action; and (2) to rigorously analyze studies on humans reporting both clinical and histological data from skin biopsies with focus on DNA damage, proliferation, apoptosis, oxidative stress, impact on collagen, elastin, immune cells, and pigmentation. We conclude that blue light therapy is safe for human skin. It induces intriguing skin pigmentation, in part mediated by photoreceptor Opsin‐3, which might have a photoprotective effect against ultraviolet irradiation. Future research needs to unravel photochemical reactions and the most effective and safe parameters of blue light in dermatology.

Spectral Characterization of a Blue Light-Emitting Micro-LED Platform and Microbial Chromophores for Therapeutic Applications in Skin Conditions

“…Blue light (380 – 500 nm visible light) has high potential as a safe, non-invasive, and relatively cheap approach for the manipulation of microbial communities due to its microbicidal properties (34). However, studies employ poorly characterised light sources with variable intensity and spectral properties, resulting in conflicting findings (35). We present evidence of the thorough characterisation of a μLED illumination platform for in vitro studies.…”

Illuminating microflora: shedding light on the potential of blue light to modulate the cutaneous microbiome

“…Blue light has garnered considerable attention due to its capacity to manipulate dendritic cell activation, resulting in modulation of cell proliferation and inflammatory responses in vitro ( Liebmann et al., 2010 ; Fischer et al., 2013 ). In vivo studies demonstrated that full body irradiation with blue light (400 - 500 nm) resulted in improved pruritus (urge to itch), quality of life and reduced hydrocortisone use ( Uzunbajakava et al., 2023 ).…”

“…These potentially undesired effects span erythema (sunburn), photoaging, decreased skin hydration, elevated melanin production and subsequent hyperpigmentation ( Mahmoud et al., 2010 ; Duteil et al., 2014 ; Duteil et al., 2020 ; Kumari et al., 2023 ). However, the latter has also been hypothesized to carry a photoprotective effect against subsequent UV irradiation by some groups ( Uzunbajakava et al., 2023 ). The exposure to blue light has only increased as technological advances have resulted in our constant exposure to blue light from screens and mobile devices.…”

“…The exposure to blue light has only increased as technological advances have resulted in our constant exposure to blue light from screens and mobile devices. The actual irradiance and dose emitted by these appliances is far lower than those found in natural lighting and hence the impact of such appliances on the skin is minimal, if present at all ( Arjmandi et al., 2018 ; Duteil et al., 2020 ; Kumari et al., 2023 ; Uzunbajakava et al., 2023 ). Nevertheless, exposure to such devices, peaking around ~440nm via visual pathways, has been shown to manipulate circadian rhythm through excitation of melanopsin located within retinal ganglion cells ( Wahl et al., 2019 ).…”

“…Blue light is strongly attenuated by the skin haemoglobin and melanin in comparison to wavelengths within the red and near-infrared spectra. Still blue light can reach relatively deep targets in the skin, including the hair follicle bulge at a depth of approximately 0.5-1mm relative to the skin surface, while its intensity will be highly attenuated versus the photon density administered at the skin surface ( Figure 2 ) ( Uzunbajakava et al., 2023 ). While blue light may be most effective in manipulating surface level microbes, its efficacy in influencing sub-epidermal layers including sebaceous gland and entire hair follicles will be modulated by light attenuation by the skin.…”