When it comes to skincare protection, aside from knowing you need to smear sunscreen on every day, then reapply every two hours when you sweat or swim, there's probably not much more you concern yourself with. In fact, we're willing to bet you don't know the answers to the most common questions about sunscreen. 

Luckily, you don't have to. We gave Terrence Keaney, M.D., board-certified dermatologist and founder of SkinDC in Arlington, VA, the third degree to answer all the burning questions for you. Here's what you need to know. 

1. Sunscreens come in many forms. Are they all the same?

Some sunscreens are “mineral” (also called physical), others are known as “chemical,” Keaney says. Mineral sunscreens, made from zinc oxide and titanium dioxide, are more effective “broad spectrum” products that block, reflect, and scatter UVB (which causes sunburns and skin cancer) and UVA (which leads to skin aging and, well, also cancer) radiation. Chemical sunscreens use a combo of 15 other FDA-approved ingredients that absorb certain UV wavelengths, he adds. "Zinc oxide has the broadest coverage of UV radiation—even more than titanium dioxide—so when in doubt, pick zinc oxide," he recommends.

2. What SPF do I need?

In reality, the potency of SPFs aren't all that different from one another. SPF 15 filters 94% of UVB rays, and SPF 30 filters more than 97%, Keaney explains. Sunscreens with an even higher number offer quality protection, even if you use less of it, but there's a marginal difference between 50 and 100. However, "SPF number calculation are performed with a large quantity of sunscreen that most people typically don't apply: a full shot glass for the whole body," he says. Your best bet is to use a broad-spectrum sunscreen with SPF 30 or greater.

3. Does wearing sunscreen clog pores? And will certain ingredients pose health risks?

Sunscreen itself hasn’t been shown to clog pores, but the base it’s mixed with could, Keaney says. Look for products marked “non-comedogenic,” which are formulated to not block pores. As for ingredients you should stray from, avoid oxybenzone. Found in chemical sunscreens, this ingredient can cause allergic reactions and damage the environment, including coral reefs.   

4. Which first: moisturizer or SPF? 

Moisturizer, then SPF. Mixing dilutes SPF, making it less effective, though. "I would avoid blending because it will only dilute the sunscreen's ingredients, reducing its protection," Keaney advises. 

5.  Are there any safe alternatives if I run out?

"If you find yourself at the beach with no sunscreen, your best options are sun-protection clothing, hats, and shade," Keaney says. There are loads of hats and clothing options with built-in SPF protection that have a distinct advantage over sunscreens: They don't need to be reapplied.   

Want some guidance on the best mineral, sport, and stick options? Click through for our six favorites.