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.)