Summer comes and goes, but UV damage remains forever.

Not to scare you s***less but the sun can have a real negative effect on your body. Sure, we’re all about baking in the sun and getting crispy AF as much as the next person. But what we’re not into is skin cancer, pigmentation, damage as well as lots of other nefarious outcomes that can come from the skin.

Which is why we need to have a conversation about SPF. That’s right, ES-PEE-EFF. It’s the product that protects your skin from the sun, which emits both harmful UVA and UVB rays.

SEE ALSO: Here’s the best men’s sunscreens to try now

We already wrote about which sunscreens we’re really into at the moment. But here’s a complete guide to sunscreen, SPF and everything you ever wanted to know, just in time for summer vacation, beach whale-ing, and living your best life under the Tuscan Sun.

First off, why TF is it called SPF?

Okay, bruh. Good first Q. At your next party, you can totally tell your friends you learned that SPF stands for “sun protection factor.” It’s basically comparing how long it takes sunscreen-protected skin vs. unprotected skin to get burned. The higher the SPF, the more protection against UVB and UVA rays.

Okay, UVB and UVA? Sounds like a college I’m applying for.

Lol. Indeed, UVB and UVA are both universities, but they’re also names for ultraviolet rays. One is a long wave (UVA), the other is short (UVB). While UVA rays penetrate the skin’s thickest layer, UVB burns the superficial layers of the skin. It’s also the key factor in the development of serious skin cancer. Remember this: every time you get burned, there’s serious damage that’s happening over time.

So, you’re saying me going shirtless on a Sunday afternoon stroll is gonna cause cancer?

Yes and no. We’re exposed to sun all the time (well, unless you live in Svalbard, Norway where there’s no sunlight for months). But continued sun damage can accumulate to skin damage. Just be warned that turning lobster red on weekends is no bueno.

But I TRULY hate that chalky, pasty, substance that’s sticky and not really thrilling to use.

We feel you. You’re talking about physical SPF. That’s why there’s also something called chemical SPFs. The latter goes on smoothly, without any white, pasty substances, and works just as well. It really depends on what you’re looking for.

Here’s the big difference, according to Dr. Marisa Garshick from Manhattan Dermatology and Cosmetic Surgery.

What is a chemical SPF and what is a physical? I totally thought there was ONE KIND of sunscreen!

Same. But when we found out there were two kinds, we totally felt enlightened. Here’s Dr. Garshick’s explanation:

“Chemical sunscreens are sunscreens that contain ingredients such as oxybenzone, avobenzone, octisalate, octinoxate among others) which absorb UV radiation and convert it to heat to prevent DNA damage from occurring,” she tells us. Basically, this means that sun is absorbed into the skin and then zapped back out into the universe as heat.

“Physical sunscreens are sunscreens that contain ingredients such as zinc oxide or titanium dioxide which actually reflect UV radiation, thereby actually blocking the suns rays from penetrating the skin,” she says. You can imagine this as a basic umbrella that blocks the rays from getting in.

So which one’s for me?

Here’s the simple answer: if you have sensitive skin, go for the physical. Chemical will create heat in your skin and can cause breakouts for some people. But if you hate chalky, pasty, thick creams, go for chemical. It’s great for those who don’t have sensitive skin. But while physical is an immediate umbrella of sorts that you can wear and walk out the door with, chemical takes about 20 minutes to seep into your skin and work its magic. Just make sure it’s broad spectrum!

Broad huh? Broad what?

 “Broad spectrum refers to the fact that the sunscreen provides protection against both UVA and UVB radiation, which together can contribute to sunburn, skin cancer and aging,” says the good doc. “It is important that you choose a sunscreen that indicates it is broad spectrum in order to get full coverage and protection.” Long story short: just make sure you buy a product with BROAD SPECTRUM written on its label.

Cool. Now that I’m totally wearing SPF, do I have to care about that number? What does it all mean?

Good rule of thumb: the higher the number, the greater coverage. But know that unfortunately, nothing will provide you with 100% of coverage. Here’s a really good graph from the good folks at Coola.

(Photo courtesy Coola)

As you see, though SPF is great, the lower the number, the less coverage. The most anyone will ever need is an SPF 50. Anything above is really extra and totally just a marketing scheme.

In fact, studies showed that people who used an SPF above 50 were still sunburned. “Even when using SPF 100 under ‘real world’ circumstances, people still experienced a sunburn,” says Dr. Garshick.

So I’m gonna go for an SPF 50. Do I apply in the morning and just not worry about it any more?

That would be awesome if you invented something that actually had staying power than for a couple of hours. Unfortunately, you have to reapply every 2 hours or so, no matter if it’s a physical or chemical SPF.

Here’s some other very worthwhile tips from Dr. Garshick:

-Reapply every 2 hours; even more frequently with heavy perspiration, swimming or toweling off.

-Make sure to look at the water-resistant label and timing, particularly if will be active or swimming

-Apply liberally. You should be applying the equivalent of a full-size shot glass with each application (Editor’s note: OMFG that’s a lot!). It has been found that people often apply only 25-75% of what should be applied to reach the actual SPF rating.

-Don’t forget your lips, which can also suffer from sun damage and there are products out there that are specially designed for the lips.