Which type of UV radiation is primarily responsible for skin melanin activation?

UVB radiation is the primary type responsible for activating skin melanin. When skin is exposed to UVB rays, it triggers the production of melanin, the pigment that gives skin its color and helps protect it from further damage from the sun. This melanin production is part of the skin's natural defense mechanism, helping to absorb and reflect the harmful effects of ultraviolet radiation.

In contrast, UVA radiation penetrates the skin more deeply and is associated with aging and photo-damage but does not significantly contribute to the initial melanin activation. UVC radiation is mostly absorbed by the Earth’s atmosphere and doesn’t reach the surface, making it negligible in terms of skin effects. UVD is not commonly recognized in the context of UV radiation categories related to skin effects. Hence, UVB is the key player when it comes to stimulating melanin production in response to sunlight exposure.