What is sunlight made of?
Sunlight is made of bundles of energy, called photons, moving in space in the form of electromagnetic waves (or radiations) whose wavelength determines the quantity of photons the body can use. Thus, the positive biological effect of a radiation depends only on its wavelength.
According to a classification based on wavelengths, sunlight is made up of ultraviolet rays (UV), visible rays (violet, indigo, blue, green, yellow, orange, red) and infrared rays (IR).
Ultraviolet rays (UV) are responsible for the greatest phototherapeutic benefits of light; ultraviolet rays can be further divided, depending on their wavelength in nanometers (nm), into UVC rays (100-280 nm), UVB rays (280-315 nm) and UVA rays (315-400 nm).
Why do we tan?
The hyperpigmentation deriving from sunlight has been known for ages: tanning derives from exposure to the intense natural light of summer , of the Tropics or of the mountain peaks.
UVB rays in it are able to reactivate the production of the missing melanocytes and, therefore, also melanin production in vitiligo skin patches. UVBs –except for the Tropics and the mountains- can be found just in summer sunlight (0.2% and, in industrialized areas, i.e. a great part of the Earth, as little as 0.02%).
However, such quantities can still have a positive effect if the exposure to sunlight follows a sufficient number of Ratok®therapy sessions (using the suitable precautions, sunlight exposure is strongly recommended in case of vitiligo). IR and UVC rays are of no interest in relation to vitiligo.
UVA rays (4.8% of sunlight) just increase the color intensity of the already present melanin. They cause a quick but temporary tanning, but, as they’re not able to promote melanogenesis, they can’t re-pigment vitiligo patches. Moreover, UVA rays penetrate as far as the second skin layer, the dermis, causing the well-known damages of photoaging.