How often do i need to apply sunscreen?

Lots!: Put on sunscreen about 20 minutes before heading into the sun. Then reapply every 2 hours (more often if you get sweaty or wet). Make sure you use a broad spectrum sunscreen that protects against both uva and uvb rays. Also- remember your hat and sunglasses!

SPF X 10 min + ftr : A simple rule of thumb is SPF x 10 min is basic protection (spf15=150min) but there are many variables.If one is sweating, the material washes off. Some stick better than others, but the term waterproof means you can dunk an arm in the water up to two times & it still works, after three it can be gone & still labled waterproof.