Monday, April 7, 2014

Is 1/4 tsp Enough Sunscreen for Your Face?


Hopefully, you guys have all made your dermatologists proud motherfuckers by wearing adequate amounts of sunscreen all winter long, and this post is just a helpful reminder. For the rest (and presumably the majority) of you, go buy some more sunscreen! 


If you followed my sunscreen series at all last summer, you probably remember that sunscreen can't be applied all willy nilly! The amount of sunscreen you use is essential if you're aiming to get the advertised SPF. In particular, you need to apply sunscreen at an area density of 2 milligrams per centimeter squared. This translates to a lot of sunscreen-- 0.04oz/1.13g for a face alone. I also calculated out my body area and found that I needed about 1.063oz to protect my whole body. (If you're larger than I am, you would need more.)

Sadly, area density isn't converted to volume without more specific info about your sun goop. Still, 1.063oz had a really convenient volume approximation: it's about the same as a shotglass of sunscreen. If you are applying a shotglass worth of sunscreen, you're probably in the approximate range of SPF protection that you're aiming for. Unhelpfully, 1.13g does not have such a convenient volume rule of thumb.

...or so you might think.



All over the internet machine, there is a specific recommendation: use 1/4 tsp of sunscreen to cover your face. Although it's oft repeated, I couldn't find an original source for how this was calculated, so I decided to do some fact checking with my handy dandy scale.

The sunscreen I'm using for this test is the Neutrogena Sensitive Skin Broad Spectrum SPF 60+ Sunscreen. It was not picked for any particular reason; it's simply the sunscreen I am using at the moment. I mention it, though, because there's a little fuzziness here, since not every sunscreen is going to have the exact same density. If you are using a sunscreen that is dramatically more or less dense than my sunscreen, my investigation might not be fully applicable.

First, I measured a perfect, flattened out teaspoon, the way I might measure if I were baking a cake. I got... 0.995g. Whomp whomp whomp... remember, we were hoping for 1.13g. In other words, close, but no cigar. We're at 88% of the mass we were hoping for.

Next, I tried out a heaping quarter teaspoon, the way I might measure when the waffle recipe says, "1 tbsp sugar" and I'm like, 'fuck you recipe, I like my waffles sweet'. I got a much happier 1.481g, more than the desired 1.13g!

So, what's the verdict? If you already have a quarter teaspoon beside your vanity reserved for sunscreen measurement purposes, choose a heaping teaspoon over a flattened out, perfectly measured, quarter teaspoon, which will probably be too little sunscreen. (And if you have a teaspoon beside your vanity for sunscreen measurement purposes, I know you care.) If you want to purchase a measurement spoon for sunscreen, though, I'd go with a 1/3 tsp, which will put you in the "slightly too much"/"better safe than sorry" sunscreen category. [(4)(0.995)=(3)X, X=1.326g, so 1/3 tsp should be closer to 1.326g.]

For those of you who are slightly less precise, I'd just give your measuring spoons a quick glance and squeeze out a blobby approximation. (Which is what I do.)

34 comments:

  1. Hey Robyn! This has been bothering me for ages, I use a sunscreen called Skinnies, http://www.gotskinnies.com/ with the tagline "a little goes a long way". They actively encourage you to use less because there's no water in the formula. I'm stumped. Does water have anything to do with it? Should I actually use less, or ignore them and keep at 1/4 tsp?

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    1. I would want to know what area density they tested it at before I would use that sunscreen at all. Industry standard is 2 mg per cm squared. The only reason I would give them the benefit of the doubt at ALL is because they are a New Zealand/Aussie company so they MAY have different laws and procedures. They're saying that it's a 1:5 ratio, but that would be such a low amount that I doubt you would get even coverage even if that claim's not crap.

      The percentage of the active ingredients are not on the website. If they were, it would be possible to use a sunscreen calculator to estimate SPF.

      For the record, they also have some other obvious terrible bullshit on the site: "Conventional sunscreens contain 50-70% water, which is why they can take up to 20 minutes to dry, leave you looking white and greasy, and wash off when you swim or sweat." This is just... not... true.

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  2. http://amelialiana.com/2014/04/morning-skincare-routine/ Here's a beauty bullshit that will make you crazy and make a mockery of the concept of SPF standardization. Start about 5:45 - it's the Goldfaden MD "spray" and her notion of it that is like, WHAT?

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    1. She is definitely not getting enough SPF there, but I'm not comfortable calling out individual people.

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  3. THANK YOU Robyn for this! I keep hearing that 1/4 tsp. rule of thumb, but never with any evidence that it's an appropriate method.

    I do have a question though: I also see a lot of folks on the internet claiming that moisturizer with SPF is a bad idea because you'd have to use so much more moisturizer to get comparable coverage to a sunscreen. But shouldn't the SPF of the moisturizer also be calculated at 2mg/cm2? Or do they just add sunscreen to the moisturizer, effectively diluting it? If you have any ideas it's more than I know!

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    1. I'm curious about this too! But I always stick to the logic that I never use 1/4tsp+ of moisturizer anyway (especially not during the day!) so I better wear sunscreen anyway just in case.

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    2. This!! I'd love you to do this. I've been trying to figure it out. I think I use too little because face cream is expensive. I try to layer it on (face lotion, bb cream/foundation and powder) hoping it will keep me covered. I hope some of your readers are kidding they don't think we need sunscreen. Every person over the age of 50 I know in my home state of Rhode Island has had skin cancer cut off them. Personally my d├ęcolletage looks way older than the rest of me and I'm bummed younger me thought trying to tan my weirdly un-tenable Italian skin was a good idea.

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    3. I don't see any reason why moisturizer with sunscreen would be a bad idea if you are comfortable applying that amount of moisturizer.

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  4. Hah! I do the blobby approximation thing. Although, have been reading that re-application is more important. I never reapply on my face because a lot of the time I'm wearing makeup and who's got time for that? For a while I was quite good about it and used this Peter Thomas Roth tinted powder sunscreen but it was too much of a faff (plus when I take the cap off SO much powder comes out and I start choking on it).

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    1. I don't know if it'll help you much, but ELF has a sunscreen powder that's 45spf and is just a translucent powder. I really like it for touchups. $6 too.

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    2. Ooh thank you! We just got ELF in New Zealand, so I'll need to check this out. Well, as soon as they restock the shelves -- they were cleared out at my closest store.

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    3. You might want to read this-- http://www.brightestbulbinthebox.com/2013/05/drugstore-dupes-to-test-peter-thomas.html

      And, more importantly, THIS-- http://www.brightestbulbinthebox.com/2013/06/how-much-is-2-milligrams-per-centimeter.html first. Powder sunscreen is definitely not enough alone!

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  5. Interesting! Here's the source for the 1/4 teaspoon measurement: http://www.futurederm.com/2013/04/26/how-much-exactly-is-2-0-mgcm2-the-amount-of-sunscreen-necessary-to-achieve-the-labeled-spf-rating/

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    1. They're mostly right, but even their calculations show that's not quite enough, and that's making the assumption that 1g=1ml, which isn't necessarily true.

      If people are doing a quarter teaspoon they are doing better than most, but I know a lot of people who are anal about sunscreen, so I thought the post was relevant either way. :)

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    2. Oh, yeah, totally useful. Just thought you might like to know where it was coming from. I use a clear liquid sunscreen (Kinesys), which is amazing, but it's really hard to estimate how much I'm using. I guess I could get out a measuring spoon, but the formula is totally different from creams, so I'm not sure if it would matter.

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  6. Wow, today I learned that I use WAY too much sunscreen. I didn't know the measurements but just knew that most people don't use enough, so I was seriously putting about two teaspoons on every morning (and rubbing it in for like 10 minutes straight).

    No more, though! This is actually really exciting for me, haha.

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  7. I wish my skin didn't hate most sunscreens so much. It seems to handle the physical blockers OK, but the chemical ones just irritate the crap out of my eczema.

    And I live in the Hemisphere of No Ozone Layer (thanks, northern hemisphere industry :-P).

    Mostly I just do what I can and run from shadow to shadow with a jacket or umbrella over my head.

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    1. I do really like that Neutrogena sunscreen written in the post, if you can get your hands on it.

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  8. Hum. This is something I've never been able to buy into. I mean, our parents walked around all day everyday without sunscreen. Our grandparents walked around all day everyday without sunscreen. These people lived through a hole in the ozone layer, and yet have never demonstrated any ill effects from sun exposure. I'm sure some people have a sensitivity to the sun and may be prone to skin cancer, but it seems like that would be the exception rather than the rule. I mean, if no one in your family has ever had any kind of skin cancer or growth, is it really something you need to obsess over?
    I just don't see why so many people go apeshit over sunscreen. I know you get wrinkles a little earlier, but…we're all gonna get wrinkles anyway.

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    1. While risk varies for individuals (natural skin color, family history, time spent in the sun and number of sunburns), skin cancer unfortunately isn't rare or the exception. It's 90% caused by UV radiation from the sun, it's the most common cancer, incidence is still rising, and 40%-50% (!) of Americans who live to age 65 will get it in some form. Although most skin cancers are basal cell and squamous cell carcinomas, which aren't usually life-threatening (unlike melanoma), it's really not fun to have them cut out of your face, and they do scar (personal experience with family members here...)
      Plus, UV exposure is actually responsible for a large amount, 80%, of visible facial aging signs...not that anyone is required to care about that, but I'm sure beauty blog readers care more than the average person! Which is why we collectively tend to be apeshit about it. :)

      (Sources: Skincancer.org, Flament F, et al, in Clin Cosmet Investig Dermatol. 2013;6:221-232--actually this study was done in Caucasian women so it might not be generalizable, but it's the source of the often-seen "80% of visible aging is caused by the sun" statistic.)

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    2. I am probably older than the general demographic for this blog, but my grandma totally got skin cancer from sun exposure not once, but twice. My BFF is ten years younger than I am and her mom just had skin cancer removed recently.

      Living in Seattle I am nowhere as good about applying sunscreen as I should be, but this week in Disneyland I am putting sunscreen on the whole family, plus making everyone wear hats.

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    3. I question your premise -- I have multiple older relatives who have had skin cancers removed, including a melanoma in situ. My father in law has had five squamous cell tumors removed. My great-uncle Hugo is COVERED with skin cancer scars.

      Also, in previous generations? People wore hats when they were outside. That's what I mostly do; my skin really does not like sunscreen, so I wear a giant floppy hat.

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    4. "I mean, our parents walked around all day everyday without sunscreen."

      Yeah, they did. My mom's had skin cancer like five times.

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  9. Thanks! I haven't actually been measuring sunscreen and should really be more careful, so I'll try this!

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    1. Cool! Hope it works well for you!

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  10. This was super interesting but I'm not going to lie, I'm terrible at remembering sunscreen.... I barely ever wear it.

    http://mattekat.blogspot.ca/

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    1. GET IT INTO YOUR ROUTINE! Once it's burrowed its way in there, it's impossible to forget.

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  11. God, I use so much sunscreen. Probably 2/3 of a teaspoon for my face, 1/3 for my neck, and another teaspoon or two for my forearms.

    It seems to sink in pretty well though, and rather too much than too little. I've been doing it since I was 14 (the one minor benefit of my early teens goth phase) so hopefully my skin will be lovely at 50.

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  12. Okay so here's what I very very badly want to know: Sure, we need to use a shotglass for our whole bodies if we want to get the advertised SPF. But do we really need the advertised SPF?

    I know that some of this will vary, more melanin equals less burny, etc. But the SPF on so many products seems really high to me.

    If it takes about an hour for me to burn normally, isn't even 30 SPF pretty much overkill? Is it that high because they know we won't put a full shotglass on? Should the question not even be "how much to not burn" but instead "how much to not damage my skin" or "how much to not increase my risk of skin cancer"? If so, how much does it take to not damage my skin? How much to not increase my risk of skin cancer? And is it true that anything over 50 or 60 SPF (I forget how much exactly) is unnoticeable in terms of its effect?

    Do a faq! :-D Pleeeeaze?

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  13. I've become an SPF nut in the past months—I've only started slathering the stuff on at the start of the year. I think I'm making up for lost time, as I've been SPF-ing the crap out of everything. Anyway, thanks so much for the post—I have no spatial skills, so can't figure out 1/4 teaspoon in relation to the usual puddle in my hand. — Sasha

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  14. I've actually been using (generous) finger tip units to estimate how much I should put, but argh! Still too conservative :(

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