Sunscreen protects skin by blocking UV radiation. It's important to use sunscreen to prevent sunburn and skin cancer. Sunscreens have two types: chemical and physical. Chemical sunscreens absorb UV rays, while physical sunscreens use titanium dioxide and zinc oxide. SPF ratings indicate protection levels. While no sunscreen blocks 100% of UV, they block most. Some chemicals may be harmful, but studies show they are generally safe. Using sunscreen correctly and applying it evenly is key. People should avoid homemade sunscreens and check expiration dates.