According to Dr. Brooke Jackson, a board certified Dermatologist and founder of the Skill Wellness Center of Chicago, "sunscreen is like the screen in your windows, allowing penetration of some rays, about 89% filter.

Sunblock is more protective. It often has physical blockers like titanium dioxide and will filter out about 97% of UV rays, giving maximum protection against the sun at an early age. We know that sunburns and large amounts of sun exposure at a young age (prior to age 18) is a HUGE risk for skin cancer later in life.

For runners -- apply sunblock from cheeks down to avoid [having] it getting into eyes and stinging.

Use SPF 30-45 for outdoor activities and re-apply every 90 minutes. Use water or alcohol based sunblock for working out to avoid clogging pores (Coppertone Sport Block is a great example)."