Ah, the healthy glow of the sun-baked traveler. The deep, golden tan. The wrinkles. The spots. The doubled risk of skin cancer.

…Yeah… or not. It’s time to slather on the sunscreen. Here are the facts on your new best friend.

A Brief History

For a very long time (read: most of human history) pale skin was fashionable. Being pale meant you were rich enough not to have to work in the fields. And, as a rule, riches dictate fashion. Both the Ancient Egyptians and the Ancient Greeks recorded using pastes and oils to block the effects of the sun.

It was during the 1800s that Ultraviolet rays were first noticed and studied (This was also the century when all the poor people started losing their horrible peasant-y tans by working in factories. But the rich people could congratulate themselves on not getting rickets, so…). By the time the 1920s rolled around, people were starting to cotton on to the fact that UV rays could cause skin cancer.

However, it was also around this time that famed model Coco Chanel accidentally made tanning the new vogue after a holiday in France. People were lying out in the sun for hours – on purpose – and they needed protection.

Formulas for sunblocks and sunscreens were developed throughout the 20s and 30s. After WWII, their use became more popular and widespread as tanning increased. Since the introduction of water-resistant sunscreen in the ’70s, we’ve been constantly improving on the properties and protection of sunscreen.

If only we’d use it correctly.

Who Needs Sunscreen?

Kids, right? Or super-pale people? Nope, it’s everyone. No matter your race, age, whether you go brown or pink in the sun – UV rays will cause damage. True, some people burn quicker than others (we’ll get to that). And if your skin contains melanin, you have some extra protection. Some. But everyone needs sunscreen, period.

Don’t believe me? (Why not? Would it help it I typed this wearing a lab coat…?) Visit the Skin Cancer Foundation, the American Dermatological Association, or just about any trusted medical source, and read what they have to say on the subject.

How Sunscreen Works

The harmful UV rays that you need to protect yourself from are called UVA and UVB rays. UVA rays cause aging effects on the skin, and UVB rays cause burning. Notice the handy alliteration there. These rays damage your skin cells and their DNA. If the DNA mutates as a result, it can cause cancer.

Look for labels that tell you the sunscreen is “broad spectrum”, which means that it is capable of protection against both UVA and UVB rays. One or the other won’t cut it.

Sunscreen relies on two main types of protection. One is the presence of inorganic ingredients such as zinc oxide and titanium oxide. These physically block the rays from your skin. The other form of protection is from organic chemicals. These absorb the UV rays and convert them to heat which is then harmlessly released. Science!

SP-What Now?

SPF stands for Sun Protection Factor. It protects you against the UVB (burning) rays. The number given on the bottle refers to the amount of extra time the sunscreen gives you before you burn. So if you normally burn within 15 minutes, an SPF of 20 gives you 300 minutes before you start burning.

This calculation is not too reliable, however. There are other factors to consider. Also, the numbers don’t add up quite the way you’d think. SPF 30 is not double the protection of SPF 15 – in fact, it only knocks the number up from 93 percent protection to 97 percent. (This is a significant change, though. Remember, that’s 4 per cent of the sun’s rays.)

SPF 50 can block up to 98 percent of the sun’s rays. But beyond that, it seems that the increasing numbers don’t mean all that much. No matter how high the number, no SPF will completely block all UV rays. And those low SPFs? The 2 to 14 range? Don’t even bother.

How Often?

So you normally burn within 10 minutes, and you’ve put on SPF 45. You should have 450 minutes before you need to reapply, right? Well, no – this basically means you have 450 minutes before you burn, provided you are wearing SPF 45 the entire time. The sunscreen itself is not going to last that long.

It is recommended that you reapply sunscreen every two hours. If you are swimming or sweating, this should be every forty minutes to an hour (Water-resistant does not equal waterproof… and there aren’t any waterproof sunscreens. If a label claims otherwise, it’s inaccurate.). If you are using a spray-on sunscreen, an hour is also a good reapplication time.

Oh – and make sure you’re getting it on a good 15 to 20 minutes before you head out into the sun. The liquid needs time to settle onto your skin to start giving you protection.

How Much?

If you are following all of the above instructions, and still burning, you are probably not using enough sunscreen. The average amount you need to cover yourself from top to toe when wearing a swimsuit is somewhere between an ounce and ounce and a half. In other words, a shot glass full. If this sounds like a lot, then you have definitely not been using enough. This is a medical recommendation – refer to the Official Science Places I mentioned earlier. And yes, they all literally mentioned a shot glass as an accurate amount. (If using an actual shot glass for measuring, make sure to wash it thoroughly before tequila night.)

Where?

Everywhere.

“Wait… do you mean put the sunscreen everywhere on my body, or wear it everywhere in the world?”

Um… yes.

That is, both.

“Where on my body?” Don’t think that getting the “important parts” is going to trick the sun into skipping you over altogether. I have seen people suffer terrible sunburn on their feet, for example (often unused to the sun after closed shoes). The last holiday I had, I burned my scalp of all places. Other forgotten spots include hands, cleavage, hairline, ears, lips, or along the edge lines of a swimsuit/shorts/etc.

In terms of “where in the world”… well, where are you going to find sun? Everywhere. You might need less protection in a cooler climate, but the clouds won’t block those UV rays. And heat does not necessarily equate to UV. (Sunburn is rife among skiers.) You should research the locations you’ll be visiting beforehand and see what kind of protection you should have.

The Right Sunscreen For You

Just like with anything else you put on your skin, it’s good to shop around. This might be especially applicable to the skin of your face. I know many women who have two separate sunscreens for their face and body.

You should consider whether you have sensitive skin, oily or dry skin (or a mixture). Perhaps you want something with an anti-aging factor. After a century of development, there are all kinds of sunscreens available.

Take your time and look around. If in any doubt, consult a dermatologist. It’s your skin – love it, care for it, and keep it healthy.