Light therapy encompasses a wide range of treatments in dermatology, ranging from ultraviolet B to aesthetic lasers and beyond. Using low intensity non-coherent light in the visible spectrum is often referred to as photobiomodulation therapy (PBT) or low-level light therapy (LLLT). These devices (often available for home use) have become popular for a variety of conditions, including wrinkles, scars, burns, vitiligo, and acne.
The mechanism of this type of light therapy has been characterized in an acne model: the photons produced during PBT are absorbed by tissues and transformed into intracellular energy, which can influence cell signaling and growth factor production while reducing oxidative damage in irradiated tissues, manifesting as anti-inflammatory and antibacterial effects. While there are some clinical studies, arguably the best evidence is in treating chronic wounds and ulcers. Importantly, the studies have tended to be very small and it is difficult to make firm conclusions.
Many atopic dermatitis and topical steroid withdrawal syndrome (TSW) patients have been trying treatments with one type of PBT with red light. This is different from UVB and appears to be relatively safe. However, we have almost no controlled evidence that it helps, and are left with anecdotes only. Currently, my thinking is that it may have some positive effect, particularly on the wound healing aspect, but may not be worth the time or energy for most patients. Importantly, many people are sold a unit being told that it is like what is done at a medical office, but it is important to know that the narrow band UVB treatments that are sometimes recommended are available with prescription only and require calibration and careful dose management as they can cause a burn.
Figure from Aggarwal & Lio, 2023.
Further reading: Aggarwal I, Lio PA. Photobiomodulation therapy and low-level light therapy in wound healing. Lasers in Medical Science. 2023 Oct 18;38(1):239. https://doi.org/10.1007/s10103-023-03909-9