How Often To Reapply Sunscreen
Ian Fortey Updated on October 25, 2022. In Beachby
Sunscreen should be reapplied according to the directions on the label for best results. You will notice that most brands, including popular ones like Banana Boat, Hawaiian Tropic and Sun Bum, recommend two different times on all of their labels – 80 minutes if you’ve been swimming or sweating while wearing sunscreen and at least every two hours otherwise.
If your sunscreen brand recommends a different time, and some may recommend less time after swimming, for instance, make sure you follow those directions. The specific directions for your specific sunscreen are always the best ones to use.
Applying and Reapplying Mineral Sunscreen
Mineral sunscreens typically need to be applied after 40 minutes of sweating or swimming. The two hour mark is also often cited on mineral labels for the bare minimum as well. Mineral sunscreens have similar directions as chemical sunscreens, but they are not exactly the same.
Every mineral sunscreen will likely tell you to shake the bottle well prior to use. This is because the minerals like zinc oxide and titanium dioxide can settle to the bottom. If you don’t shake them up you may be applying more of the binding agents and lotions as opposed to the active sunscreen. That means the reapplication time will be wrong because you don’t have enough sunscreen on in the first place.
Beyond these differences, a mineral sunscreen should also be reapplied after you towel yourself dry.
Applying and Reapplying Chemical Sunscreen
Studies have shown most people don’t apply sunscreen correctly. This is ironically because of the fact most people are likely thinking that of course they’re applying sunscreen correctly. How could you do it incorrectly? Well, there is a way.
Sunscreen directions are actually very vague. Here’s a typical set of directions you’ll see on a chemical sunscreen brand about applying and reapplying their sunscreen.
- Apply liberally 15 minutes before sun exposure. Reapply after 80 minutes of swimming or sweating, after toweling yourself dry, and at least every two hours.
That looks straight forward but there are two things to be cautious of in this simple set of directions.
- The word “liberally.” This is a very vague term that doesn’t offer a lot of insight into what the makers mean.
- The words “at least.” This is another thing people overlook or only pay partial attention to. Most websites agree that you need to reapply sunscreen every two hours, but that “at least” should be heeded. If you go over two hours, the effectiveness of your sunscreen will likely already be diminishing. Most of us don’t set a clock to ensure we get two hours precisely. In fact, most people just reapply when they remember it which may be two hours, two and a half, maybe four hours later. This can be dangerous as the sunscreen’s effectiveness is reduced.
How Is Sunscreen Reapplied Wrong?
Research has shown that most people are not meeting the manufacturer’s intended definition of the word “liberally.” And that’s understandable because it’s so vague. But, based on what research has observed, most people who use sunscreen are actually only using sunscreen in a way that offers a mere 40% of its intended protection.
This is in large part why it’s so important to wear at least SPF 30 sunscreen. If you are only achieving 40% effectiveness, then sun protection factor 30 is actually about an SPF 12. You are getting far less protection than you think, so making sure you reapply it correctly is very important.
What Is The Correct Way To Reapply Sunscreen?
In order to achieve the protection promised by the label of your sunscreen, you should be using 2 mg of sunscreen per square cm of skin. If you have a shirt and shorts on, that means you should end up using close to a shot glass worth of sunscreen. To cover your face, fill your palm until you have a blob about the size of a nickel and use that for just your face.
When sunscreen manufacturers come up with their SPF numbers, this is what it’s based on. In their tests, participants had a full 2mg per square cm on their skin. Because that’s the standard by which SPF is measured, you’ll never achieve those results if you don’t have the same amount applied.
If you use a spray on sunscreen, you should be spraying your face until you see an even sheen across all of your skin. Sounds like a lot, right? Well, turns out it’s not. We’ve all just been not using enough. In fact, users of spray sunscreens have been shown to use even less than users of lotions. That means you’d need to apply it even more often to get full coverage if you’re not applying it correctly the first time.
Most people apply less than 0.75 mg of sunscreen per square inch of skin. Since most of us don’t measure sunscreen out, most of us never realize this is happening. But if you squirt sunscreen into your palm and then rub it up and down your arm until it’s rubbed in, this is probably about how much you are using.
Why No One Tells You How to Reapply Sunscreen
There’s an interesting thing that happened when experts realized people were not using sunscreen correctly. As you may have noticed there’s not been a big push to explain exactly how much sunscreen to use, right? But something did happen – they told you to use stronger sunscreen.
The push for higher SPF sunscreens didn’t come from the sunscreen industry. It came from experts in cancer and dermatology. It made more sense to encourage people to use stronger sunscreen than to learn how to reapply more of it. In a way, this makes sense.
If you learn that you have been using half as much of something as you need to, some people will start using more, but some people may stop using it altogether. A lot of people dislike using sunscreen already, so making them use more could be counter productive. Instead of reapplying every two hours, some people may not reapply at all. They may not apply it in the first place because it’s becoming too expensive or too annoying to use that much of it.
Using a higher SPF sunscreen means that, even if you use it wrong, you’re getting more protection. That was considered more valuable than trying to explain to the masses how to precisely get sunscreen applied.
Do UV Rays Kill Sunscreen After Two Hours?
Even if you do apply sunscreen correctly, it essentially gets used up in about two hour’s time. This is something that can be hard to conceptualize. It’s a lotion you put on your skin, after all. It doesn’t fall off or evaporate, so why does it only work two hours?
It is the science of how sunscreen works that explains why it needs to be reapplied every two hours. Once on your skin, there are compounds in sunscreen that are able to absorb the ultraviolet radiation of the sun. These UV rays are chemically converted from dangerous UV radiation to a much less dangerous form of energy – heat. The heat is then dispersed into your skin and radiates away from you just like your own body heat does.
If you think of sunscreen like a layer of sponges, it’s easier to picture. You cover yourself in these little sponges and they absorb the sun. As time passes they fill up until they are completely full, which takes about two hours. At that point they are no longer effective and can’t absorb any more sun. So, after two hours, your skin again begins to absorb the sun’s rays so you need to reapply sunscreen.
How UV Works in SPF
Another reason for frequent reapplication is the inconsistency of real life. Scientists determine SPF in a lab with a UV lamp. This emits a constant, steady stream of UV rays. But SPF is relative, don’t forget. You get less UV exposure at 9 in the morning than you will at 1 pm on the hottest, sunniest day of the year. So on that very sunny day, at the peak of the sun’s intensity, you may be absorbing a lot more UV radiation in the middle of the day than you think.
So if an SPF rating of 30 means you get 30 times longer in the sun, you need to try to imagine the practical reality of that. On a normal day you may start to burn in 15 minutes. But on that day, maybe it would happen in 10 minutes. So SPF 30 would normally mean 450 minutes. Now you’re down to 300. And don’t forget, if you only have 40% of the recommended coverage, then you now only have 120 minutes, or two hours. And there’s one more thing to remember.
The UV filters in sunscreen become less effective the more they work. So when you first put sunscreen on, it’s working at peak power. As the molecules absorb UV rays, they begin to wear out faster and faster. So the longer it’s on, the less effective it becomes. And that’s why, after two hours, you’re going to need to reapply your sunscreen. The ability to filter UV rays would have diminished so much by that time that it’s theoretical lifespan, which may have started at 450 minutes, is not completely obsolete.
Mineral sunscreen works the same way as chemical sunscreen to prevent the absorption of UV rays. You may read online that this is not the case, but this is faulty information. For years we have been told that zinc stops the sun and maybe reflects it away from you and that is how it prevents sun damage. If that were the case, you might never have to reapply mineral sunscreen if you could still see it on your skin, right? So why do you need to reapply it? Because that’s now how mineral sunscreen works.
Studies have proven that zinc oxide and titanium dioxide primarily prevent UV rays from penetrating your skin by a process of absorption, not reflection or scattering. That means, just like chemical sunscreens, the radiation is absorbed into the sunscreen molecules. At some point those molecules become saturated and can no longer do their job. When that occurs, you need to reapply the sunscreen. Most mineral sunscreen manufacturers recommend the same frequency as chemical sunscreens, which is to say two hours.
Why Does Waterproof Sunscreen Need to Be Reapplied So Often?
According to the FDA there is no such thing as waterproof sunscreen. Manufacturers cannot make the claim on their labels any longer that their product is waterproof. At best, sunscreen can be considered water resistant. Based on FDA regulations, a sunscreen can be considered water resistant for 40 or 80 minutes and that’s all.
Because anything you apply to your skin is going to come off in the water, no one can legally make that waterproof claim. It gives users a false sense of safety that they will be receiving the same amount of protection when that cannot scientifically be the case.
Water resistant sunscreen and sweat sunscreen sunscreen should be reapplied every 80 minutes according to the label. If it’s mineral sunscreen, that probably drops to 40 minutes. This needs to happen if you have been swimming, if you have been sweating a lot, or if you have used a towel to dry yourself.
Some people feel like a water resistant sunscreen should last as long as any sunscreen if it claims to be water resistant. That’s basically why the FDA has these regulations against making waterproof claims in place. Look at it this way. If that sunscreen wasn’t water resistant at all, it wouldn’t even last 80 minutes. It would come off as soon as you get wet, so you could potentially have to reapply within five minutes if that’s how soon you went swimming.
Mineral sunscreens are usually on the lower end of the spectrum because of how they work. The minerals sit in a layer on your skin. Reapplying them more often makes sense because swimming, sweating and toweling off are more likely to reduce their coverage faster than with chemical sunscreens which do absorb somewhat into your skin.
Some sunscreens in Australia offer 240 minutes of water resistance, but the FDA in America does not allow for labels to make those claims. That said, Tropic Sport sunscreen is available in the US and meets those standards, even if the FDA isn’t on board with those claims just yet.
Reapplying Sunscreen After Swimming and Sweating
We know to reapply sunscreen every 40 to minutes after getting wet, but there’s a little more to it than that. If you have been swimming there’s a good chance you will towel off. That means you’re basically starting fresh and will reapply your sunscreen to dry skin. But what about after sweating?
Most of us don’t towel dry after getting sweaty, we sort of just rest and let it go away on its own. The exception is if your face gets sweaty, you may wipe it off. Your best bet for reapplying sunscreen after sweating is to blot your face with something like a towel or a bandana. You want to get that layer of sweat off of your skin before you reapply. This is especially true with a mineral sunscreen which will sit on top of your skin anyway. If you still have sweat on your face, or water from swimming that hasn’t been wiped away, you risk both diluting the sunscreen and preventing it from adhering or absorbing into your skin properly.
Many people notice that sunscreen actually makes them sweat more. This is especially true of those mineral versions again. Because you are applying a layer of something to your skin, you are effectively blocking your pores. Depending on the brand this could cause you to feel like you’re overheating and then sweat more than normal. Likewise, the act of rubbing in sunscreen can trigger your body’s response to produce more oils than normally. This is a natural reaction to the stimulation and to something filling the pores. Your body wants to get that substance out so first you may start producing oils and then sweat comes after to help clear the path. So making sure you know how and when to reapply sunscreen in these cases is important.
UVA Rays and UVB Rays Are a Danger
Learning to reapply sunscreen at the right time is important because skin cancer rates continue to rise. They doubled between 1982 and 2011 and since then the climb has been slow and steady. The public not knowing how to apply and reapply sunscreen is directly related to this. Many of us think we are protected when that’s just not the case.
The Bottom Line
Sunscreen should be reapplied according to the manufacturer’s recommendations. This is true for all sunscreens including reef safe and powder. At a bare minimum this should be every two hours. I’m no expert but I’ve always felt like, since most of us aren’t using sunscreen correctly in the first place, it’s always better to err on the side of caution. Apply it a little more frequently to ensure you’re getting the best possible protection. A little added protection is better than not enough throughout the day.
If you have been swimming or sweating, that moisture is going to cause your sunscreen to come off much faster. You will need to reapply every 80 minutes to as much as every 40 minutes. Make sure you use at least SPF 30 and make sure it offers broad spectrum protection. That will keep your skin protected from both uva rays and uvb rays. The more sunscreen you can put on at a high spf the better. As always, stay safe and have fun.