**5. Phototherapy (UV irradiation) and wound healing**

New contemporary research shows that controlled UV exposure might have some eventual benefit in wound healing and cutaneous homeostasis. The effectiveness of UV energy in enhancing biological changes depends on the chosen irradiation parameters, with maximal effective wavelength and lowest irradiation level [29]. The main mechanism of phototherapy is related to the depth of penetration. UVA, for example, has the longest wavelength and penetrates to the upper part of dermis in human skin, and UVB only penetrates down to the basal layer; however, UVC only reaches the upper part of the epidermis [30].

UV has bactericidal effect and its radiation to the skin can increase blood flow, producing erythema and epidermal hyperplasia [31]. The induced erythema via vasodilatation and inflammatory response represents the first phase of healing. In addition, UV light irradiation increases cellular proliferation in the stratum corneum [32], which can be a protective mechanism against further sunlight damage.

Although UV protection and antisolars are commonly advised during and after wound healing, it is possible that UV also affects the melanocyte redistribution and prevents the normal cutaneous response to injury [33].

It has been shown that UVC light *per se* could stimulate wound healing. UVC light enhances fibronectin and growth factors release leading to increase healing cascade and wound contraction [34, 35]. UV can promote endothelial cell proliferation [36] and augment epidermal thickness and reepithelialization or desquamation of the leading edge of periulcer epidermal cells [31].

UVC (200–280 nm) has a significant antimicrobial effect and can be used as efficient bactericide agent for treatment of acute wound infections and killing pathogens without undesirable injury to host tissue. UVB (280–315 nm) irradiation to the wound has wound healing stimu‐ lating effect and extracorporeal UVB irradiation of blood adds immune system stimulating effects too. Although UVA (315–400 nm) has specific effects on cell biologic events, it has not yet been extensively applied to wound treatment [31].

An interesting study compared the efficacy of phototherapy on wound healing in rats under the normal and high‐fat diets and revealed increased wound healing by regulating oxidative stress in rats with metabolic disorders under a high‐fat diet [37]. The efficacy of UV therapy on pressure ulcer is not clear due to eventual bias and limited number of trials available for consideration. Further research is recommended to determine possible benefit or drawbacks of this treatment [38].

While low level laser (or light) and photodynamic therapy both have considerable applications in wound care, but penetration of UV light into tissues and its efficacy is restricted. UVC and UVB can damage DNA in host cells and chronic exposure to UV can be carcinogenic. Accord‐ ingly, additional study of cellular signaling that occurs after UV exposure of tissue is needed to better indicate the risk and benefits of UV irradiation in wound healing.

### **5.1. Contraindication of phototherapy**

