Thermotherapy: What are the benefits of infrared light for the skin?

It is often suggested that infrared light could contribute to a more even complexion, acting on both pigmentation irregularities and certain persistent redness, such as those left by inflammatory lesions (post-inflammatory erythema). Indeed, this light has well-documented anti-inflammatory properties. In fact, by activating the mitochondria and increasing ATP production, red light modulates the expression of certain pro-inflammatory cytokines, such as IL-1β or TNF-α, thus helping to soothe inflammations and the accompanying redness. This is particularly interesting for individuals who have suffered from inflammatory acne and still have red marks, despite the disappearance of spots.

On the other hand, the effects of infrared light on brown spots are less well understood. It has been shown that melanocytes, responsible for the production of melanin, react to red light, but in a way that is still difficult to interpret. Indeed, some studies in vitro have highlighted a stimulation of melanocytes following red irradiation, which has been exploited in the repigmentation of vitiligo. Conversely, other studies have reported an inhibition of the activity of tyrosinase, a key enzyme in melanogenesis. These results, at first glance contradictory, could be explained by differences in irradiation protocols (wavelength, duration, frequency) and the types of cells studied (healthy or not melanocytes).

While the effect of infrared light can help to reduce persistent redness, its impact on brown spots remains to be clarified.

Infrared light is also utilised for its regenerative effects on the skin and is particularly valued for its ability to reduce the visibility of scars. These may be acne scars, post-surgical scars, or marks left by more superficial injuries. In all cases, infrared light promotes tissue repair by stimulating collagen production by fibroblasts and increasing the activity of macrophages, the cells that clean cellular debris and fight infections. These various effects follow the activation by infrared light of the TGF-β1 protein, which controls cell growth and division.

Several studies have demonstrated the benefits of phototherapy in reducing scars. Notably, the work conducted by GHERSETICH and his team with 10 women who had stretch marks. After four sessions of infrared light (wavelength = 800-1800 nm; irradiation = 8-45 J/cm2), slight to marked improvements were observed. Although the infrared light did not completely remove the stretch marks, their appearance was significantly reduced for most individuals.

Finally, infrared red light is favoured by individuals with acne-prone skin. Indeed, due to its anti-inflammatory action, infrared can help soothe the skin and reduce red spots, papules and pustules. Some studies also suggest that this light has a positive effect on sebum regulation, one of the factors behind blemishes. Lastly, infrared red light has an antibacterial action. It has indeed been shown that it can reduce populations of Cutibacterium acnes, a bacterium involved in the pathogenesis of acne. This effect does not resemble a direct action comparable to that of an antibiotic but rather a modulation of the skin's microbial environment. The heat generated by the infrared can alter the growth conditions of bacteria and strengthen the skin's immune defences, thus creating a less favourable environment for the proliferation of pathogenic bacteria.

A study conducted with 28 volunteers suffering from acne has demonstrated the potential of red light in reducing skin imperfections. The patients were treated with red light (630 nm) and infrared light (890 nm) on the right and left sides of the face respectively, twice a week for 12 sessions. A significant reduction in the number of lesions was observed on the side of the face treated with red light (27.7 ± 12.7 to 6.3 ± 1.9). A decrease was also recorded on the side treated with infrared light (26.9 ± 12.4 to 22.2 ± 8.5), but unlike other studies, this was not deemed significant.