Phototherapy is commonly used in the treatment of many common skin conditions. The effect of this treatment depends on the wavelength of the light, the frequency of exposure and the mechanism of action of the light on the skin. The radiation spectrum includes infrared radiation, (IR, 760-1000nm), visible light (400-760nm), and ultraviolet radiation (UV, 280-400nm). In the visible light spectrum there is red, orange, yellow, green, blue and violet light. Dermatology has been using more UV-free blue light therapy recently. The UVB seems to be a safer alternative than standard UV treatment.
UVB interacts with the superficial cells of the epidermis, whereas UV reaches deeper layers of the skin and affects the immune cells of the epidermis and dermis. Visible light acts deeper in the dermis but more superficially than infrared radiation. The maximum penetration of blue light is 0.07-1mm.
Chromophores are molecules that absorb light. In the skin chromophores are; endogenous nucleic acids, aromatic amino acids, urocanic acid, tryptophan, tyrosine, NADPH, NADH cofactors, cytochromes, riboflavins, porphyrins, melanin, protoporphyrins, bilirubin, hemoglobin, b carotene and water molecules. The effect of blue light is dependent on the different chromophores that are the photoacceptors.
The main and most important photoacceptors are opsins, flavins, porphyrins and nitrosated proteins.
In humans, opsins are present in various skin cells including keratinocytes, melanocytes, dermal fibroblasts and hair follicles. One of the functions of opsin is to provide the necessary environment for the absorption of light at a particular wavelength.
Blue light affects the mitochondrial function through cytochrome oxidase found in the mitochondrial membrane. Opsins are activated by blue light. There are many categories of opsins expressed in the epidermis. Once activated by blue light, the opsin receptor stimulates other receptor potentials causing an influx of calcium and this starts gene transcription. In the skin, the newly formed opsins are Rhodopsin, Panopsin and Encephalopsin. These regulate the modulation of pigmentation and melanocytes directly.
Blue light also activates flavins and flavoproteins. Once exposed, these increase reactive oxygen species twofold. This reaction has been found to induce a positive effect on hair growth by the prolongation of the anagen phase of the hair growth cycle.
Other blue light acceptors are porphyrins which are heterocyclic aromatic compounds. It has been found that irradiation by blue light excites the porphyrins and leads to reactive oxygen formation.
Blue Light Anti-Inflammatory Properties
Blue light once absorbed by keratinocytes has shown a reduction in the proliferation of these cells. The production of reactive oxygen species in response to blue light exposure causes a reduction in keratinocytes activity. This causes a decrease in inflammation and an increase of the steroid hormone production pathway which has an anti-inflammatory effect.
Blue light causes the release of nitric oxide from the nitroalbumin in the skin. It also causes an increase of free nitric oxide in the dermis. The nitric oxide affects various signaling pathways and moderates inflammatory cytokines and reduces proliferation. This demonstrates that blue light via chromophores has an impact on proliferation and differentiation.
Blue light does not have a negative effect on human skin cells. Oplander et al. showed that blue light was nontoxic to human fibroblasts. Also, small doses of blue light decreased the antioxidative properties of fibroblasts.
High does of blue light at high fluences is toxic for endothelial cells and keratinocytes. This is dependent on the dose, time and fluence. Fluence up to 500J/cm2 was not toxic.
Clinical use of Blue Light
There are studies in the literature assessing the use of blue light in the treatment of psoriasis. In a prospective, randomized, double blind study, a statistically significant improvement was demonstrated in the treatment of psoriasis using blue light irradiations. This study varied the duration, intensity and frequency of treatments. The higher number of treatments were more effective. With the group receiving seven treatments per week vs. three, complete resolution of all lesions was observed in two patients. Overall, there was a significant decrease in all patients treated.
- Atopic Dermatitis and Eczema
Three studies were investigated using blue light in the treatment of atopic dermatitis and eczema. Focal blue light was given three times a week for four weeks and the outcome showed significant clinical improvement. In another study, 36 adult patients with severe atopic dermatitis were give total body blue light therapy. At 15 days, and at 3, and 6 month intervals, a significant decrease of disease severity was noted. The authors concluded that blue light is safe and effective and improved quality of life scores in the treatment of atopic dermatitis.
Many studies have demonstrated the beneficial effects of blue light treatment in acne vulgaris. The main reason is that the positive effects is related to the reduction of follicular colonization by Propionibacterium acnes. When compared to red light therapy, the blue light significantly inhibited sebocyte proliferation. The wavelength of the blue light downregulated the lipid production. This phenomenon that blue light interferes with lipid metabolism suggests the potential in acne treatment by inhibiting sebum formation.
- Actinic Keratosis
Painless photodynamic therapy is a regimen that employs simultaneous aminolevulinate incubation and blue light treatment. Significant post inflammatory response was noted but excellent results were noted.
- Photodynamic Therapy
A method of treatment that uses visible light, including blue light, is photodynamic therapy. It is currently being used for nonmelanoma skin cancers and actinic keratosis. The use in most areas of dermatology is rapidly expanding. It is necessary to apply a photosensitizing substance followed by light irradiation. The reaction leads to the formation of reactive oxygen species and as a result, destruction of the targeted cells. The best spectrum of wavelength for this reaction is blue light. The penetration of blue light into the skin is very superficial making it idea for nonhyperkeratotic actinic keratotic therapy.
Phototherapy is an important method of dermatologic treatment. The main factors involved in this response of cells to light are nitric oxide and reactive oxygen species. Blue light is an ideal wavelength as it is superficial and relatively safe. Blue light induces an anti-inflammatory and anti-proliferative effect. Itching is common in skin diseases and affects the quality of life. Blue light modulates this symptom and increases quality of life scores.
Conflicting studies have demonstrated negative effects of blue light but these side the effects can be attributed to significant length of treatment times, fluence and duration.
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Photochem Photobiol Sci 2019 Aug 1;18(8):1877-1909 PMID 31183484
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