Guwahati, Feb. 24 -- When choosing a sunscreen, the SPF number tells you how well it protects your skin from harmful UVB rays, which cause sunburn and increase the risk of skin cancer.

Sunscreens come in different SPF levels, such as SPF 30, SPF 50, SPF 70, and SPF 100, and each offers varying levels of protection.

SPF 30 blocks about 97% of UVB rays, which is enough for most people if you're doing regular outdoor activities. For example, if your skin would burn in 10 minutes without sunscreen, SPF 30 allows you to stay in the sun for about 300 minutes (5 hours) before burning. It's a good choice for daily use, like running errands or short walks, but remember to reapply it every two hours or more if you're swimming or sweating.

SPF 50...