UVB
Definition
UVB (Ultraviolet B) rays are medium-wavelength ultraviolet radiation (280-320 nm) that primarily affects the epidermis, the outermost layer of the skin. UVB rays are the primary cause of sunburn and play the most direct role in the development of skin cancers, including melanoma. They also stimulate melanin production (tanning) and are responsible for vitamin D synthesis in the skin. Unlike UVA rays, UVB intensity varies significantly by time of day (strongest between 10 AM and 4 PM), season (strongest in summer), altitude, and latitude. UVB rays do not significantly penetrate glass. SPF (Sun Protection Factor) specifically measures a sunscreen's ability to block UVB rays. While UVB protection is crucial, it is not sufficient alone — broad-spectrum protection covering both UVA and UVB is necessary for comprehensive sun safety. Chemical UVB filters include octinoxate and octisalate, while zinc oxide and titanium dioxide (mineral filters) block both UVA and UVB.
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