To avoid sunburn apply sunscreen with what amount of SPF?

To effectively avoid sunburn, it's recommended to use sunscreen with a minimum SPF of 30. This level of protection blocks about 97% of UVB rays, which are primarily responsible for sunburn. For extended outdoor activities, reapply every two hours or more frequently if swimming or sweating. Always choose a broad-spectrum sunscreen to protect against both UVA and UVB rays.