If your skin already has some tan, you can let Sola take that into account by selecting your level of existing tan via “Present tan”.
Remember not to confuse “tan” with “skin type”. Tan is the dark pigmentation that human skin develops through melanogenesis – new melanin production – as defensive reaction to UV exposure from the sun or other artificial sources such as tanning beds.
Melanin absorbs up to 99.9% of UV radiation and therefore may serve a protective role against UV rays by diverting them away from other cells. The efficacy of melanin as a sunscreen is assumed to be between 1.5-3.0 SPF, up to 4 SPF.
Various people produce variable amounts of melanin, while some individuals, such as with skin Type I, have extremely little or no melanin synthesis in their bodies.
There is more to melanin than its photo-protective properties, however, and a better understanding of its benefits versus risks is still desired.
Until then, when determining how much tan you already have and selecting it through “Present tan”, use common sense and always err on the side of caution.