11 research backed tips to get the most out of your sunscreen!

Now that it’s Spring (though it’s been snowing in Toronto…), I thought I would share some sunscreen tips1 to help you use it better this Spring and coming Summer!

Most people don’t apply enough sunscreen! Across multiple studies people only apply ¼ to ½ the amount needed for the protection on the sunscreen’s label. 2

You may have wondered why the US FDA and other organizations keep the amount needed for SPF testing so high, as it turns out 2.0 mg/cm2 is a bit of a sweet spot when it comes to reproducibility and reliability of the results. 3

Any easy way to help get the amount needed on the skin is to apply your sunscreen twice. Apply a layer, let it dry, then apply a second layer. This method is recommended by the Japanese Ministry of the Environment. 4

Try not to rub your sunscreen too much when you apply it, one study found that vigorous rubbing actually reduced the SPF by 25%. They think it was because the sunscreen was being rubbed off onto the hands. 5

You should wait at least 10 minutes before putting on or taking off clothes, to allow the sunscreen to dry and to prevent the clothing from wiping it off the skin. 6

The WHO recommends reapplying your sunscreen every two hours. Realistically most of us won’t do that, but you should aim to reapply your sunscreen at least once, and especially after physical activity or swimming and bathing. 7

Reapplying your sunscreen just once can reduce your risk of sunburn by 2 to 3 fold! While there’s differing advice on when to reapply, aim to do it at least once throughout the day. 8

One study found that only 60% of the applied sunscreen was still on the skin after 4 hours of wearing clothes, physical activity, and bathing, and only 40% after 8 hours. 9

If you’re on the beach, be aware that sand can remove sunscreen from the skin! Up to 59% could be potentially removed by laying on the sand. 10

Make sure to apply your sunscreen before UV exposure! One study on people on vacation found that they were, on average, getting 100 minutes of UV exposure before they applied their sunscreen! That was almost 30% of the amount needed for a sunburn in some cases. 11

A high SPF sunscreen can help make up for not applying enough. In an experiment, an SPF 100 sunscreen applied “normally” (which is to say, not enough) offered an SPF of 27. 12

…and a bonus tip! While the above animation is super-cute, it’s not super accurate. Sunscreens (both physical and chemical) don’t protect our skin by reflecting and scattering UV energy. Sunscreens attenuate the UV energy, absorbing it and turning it into less harmful energy – most often in the form of heat. Titanium dioxide and zinc oxide do reflect some of the UVA wavelengths, but they reflect much more in visible light spectrum, which is why they can leave a white-cast on the skin – micronization can help reduce this effect! 13

I hope you’ll find these tips helpful this Spring and Summer (and all-year round!), not only does reducing UV exposure slow down extrinsic ageing, hyperpigmentation of the skin, and the formation of broken capillaries, it also reduces our risk of certain types of skin cancers and helps prevent the immune suppression caused by UV – it’s win-win really!

For everyday sunscreen, how high should the PPD (UVAPF) be? I’ve been on the hunt for a new sunscreen, so I’ve been thinking about this a lot!

Hi @wormspoor,

Thanks for the question! I’d recommend that SPF and UVAPF are similar. So if a product’s SPF is 30, the UVAPF should be around 30 as well.

Why? This best mimics the reduction in UVA and UVB that shade provides.


As well this gives you a better idea of how much protection from the entire UV spectrum you’re getting. Imagine you’re using a sunscreen with SPF 50+, but only UVAPF 10. While you’re not sunburning, you’re still exposed to a good amount of UVA energy – this is why people are often confused when they develop a tan despite wearing a very high SPF.

P.S. PPD is just one of the methods used to determine UVAPF, it involves human subjects and compares how much protected vs unprotected skin darkens. Other methods involve measuring transmittance in the UVA wavelength bands.


How much powder foundation you need for the labelled SPF


— Figure 29-5 from Cosmetic Dermatology: Principles and Practice, 2nd Edition by Leslie Baumann

All products with an SPF or UVAPF are tested at the exact same amount, 2 milligrams per each square centimetre of skin (2mg/cm2). If you’re just dusting on your foundation or powder with SPF, to matte the skin or provide minimal coverage, you’re not getting the SPF/UVAPF on the label.

I’d recommend that you use a sunscreen (about ½ a teaspoon for the face and neck), let it dry (about 15 minutes), and then apply your powder for best protection.

There are newer sunscreens that contain primer ingredients like silicones and hydrogenated polydecene built-in.

P.S. Where’s the ½ a teaspoon for the face and neck recommendation coming from? Estimations – two of them. The first estimation is the density of an average sunscreen, and the second estimation is the average area of a face. It’s not accurate for everyone, but the exact amount (2mg/cm2) is difficult to translate!

Hi Stephen! I love your work, I’ve been using the Bioderma Photoderm, partly because of your recommendation

…but I can’t seem to get rid of the white cast. I know you shouldn’t mix mineral powders with sunscreen, but is there any reason I can’t mix unadulterated cocoa powder with it to create a tint? Thanks for any thoughts!


I’d really advise against this. Part of the protection offered by sunscreen is how evenly they can distribute the sunscreen chemicals on the skin.

Think of a crowd of people with umbrellas in the sun. If they’re all evenly distributed, very little sunlight will hit the ground…but if they’re clumped together, there’ll be more areas where the sunlight can pass through.


Sunscreen chemicals work in a similar way.

By mixing something like cocoa powder into a sunscreen, you can create areas of high sunscreen chemicals and low sunscreen chemicals – creating uneven coverage. Manufacturers use mixers with high shear and force to make sure everything is distributed properly.

If you’re getting a white cast, I think the best way to fix it is to apply your sunscreen…allow it to dry (15 minutes), and then apply a foundation or tinted powder on top!

Bioderma (and many other sunscreen brands) also makes tinted versions of their sunscreen, so you don’t have to worry about the white cast or uneven mixing!

I personally also use their mineral sunscreen compact, it comes in two shades (Claire/Fair and Doree/Golden). I’ll sometimes use the Fair all over, and Golden as bronzer/contour. Shiseido also offers a UV Protective Compact in 9 shades, that you can layer on top of your sunscreen. Hopefully you can find a shade that works for you, if not, a foundation powder with SPF like BareMinerals Ready SPF 20 Foundation will work as well.

I’ve shared an experiment before about titanium dioxide and pigments destabilizing avobenzone, however this is more important for manufacturers as the degradation takes course over a long period of time (1 week in the experiment) and requires constant UV exposure.

P.S. I wouldn’t recommend using a compact as your only sun protection, you still need the recommended 2mg/cm2, and it’s more difficult to gauge how much you’re applying when it’s coming off of a pan!

Hope that helps 🙂


Hello! I just found your blog and I really love it! And I already have a question. :)

… Basically I have a question about the last question you got. The person who asked mentioned that we’re required to use 1/2 teaspoon of sunscreen for the face alone and now I’m a little confused because I’ve thought that we “only” need 1/4 of a teaspoon? Or about 1.25 ml? Is that wrong? I’m sorry for asking, I’m just always worried about not using enough product to get the proper protection.

Great question, thanks for asking @naevery 🙂

It’s not right, and it’s not wrong…it depends!
Let me explain 🙂

The density of sunscreen used in SPF testing is always 2 mg/cm2

That means for every square centimeter or skin, 2 mg of sunscreen is applied.

This is easier to do when testing, because it’s done on the back where you can draw a 30 cm2 square and apply 60 mg to it.

Figuring out the area of the face is trickier.

The ¼ teaspoon or ½ teaspoon or 1.25 ml are based on two estimates.

The first estimate is the average area of a human face, and the second estimate is the average density of a sunscreen. Remember that ml is a measurement of volume, it provides no information about weight.

Water at 4°C has density of close to 1. 1 ml of water will weigh about 1 mg. However, oil for example has a lower density, 1 ml of oil won’t weigh 1 mg, it might weigh 0.8 mg (depending on the type of oil).

That makes things more complicated, because you can’t assume that 60 ml of sunscreen will weigh 60 mg, it might weigh 65 mg or 55 mg.

So the ¼ teaspoon, or ½ teaspoon are just estimates for an estimated human face, and an estimated sunscreen density.

These researchers for example used a beer bottle cap to measure out sunscreen.

So in order to know how much sunscreen, exactly, to apply you’ll need two measurements. The density of your sunscreen, which you can take by measuring out, say, 10 ml of sunscreen then weighing it. You’ll probably want a jewelry scale that has 0.001 g accuracy, and to measure a few times and average your measurements!

Finding out the area of your face is more difficult.

There are studies where people are told to apply sunscreen, and how much they’ve applied is weighed. It usually ranges between 0.5-1.5 mg/cm2, when they’re unprompted about applying 2mg/cm2. Their recommendation is to have people apply their sunscreen twice, instead of worrying about ¼, ½ teaspoon.

It’s up to you to how you decide to apply your sunscreen. Whether it be weighing it, measuring out the volume, or applying it twice, it’s better to err on the side on more for sun protection!

For Reference: ml = milliliter, mg = milligram, cm = centimeter, g = gram, and 1 mg = 0.001 g

Hope that helps!

Hi Stephen, I had a question for you about the UV protection in products like tinted moisturizers

…foundations, BB and CC creams. I see that they’re rated as highly as the straight sunscreens/sun creams. Theoretically, if we used the required 2mg/cm2 (1/2 tsp) of these products for the face, will they give the same level of protection as the straight sunscreens/creams? I’m asking because I’m wondering if I could be relying on a watery serum foundation for the entirety of my sun protection.

Yup! Anything that has an SPF is tested the same way.

While the US FDA, Colipa/ISO methods have a couple differences, it is always at the density of 2mg/cm2.

As long as it has an SPF rating, and you’re applying it at that density, you can be assured you’re getting that SPF – whether it’s called a serum, moisturizer, sunscreen, face pack, you name it!

Note of Interest: Only people with Skin Types I, II, or III are eligible to participate in the US FDA’s sunscreen testing protocol.

(I) Always burns easily; never tans (sensitive).

(II) Always burns easily; tans minimally (sensitive).

(III) Burns moderately; tans gradually (light brown) (normal).

Thanks for the question 🙂