Monday, June 24, 2013

How much is 2 milligrams per centimeter squared? Part Three

[For those of you who aren't faithful readers, the first part in this series, which deals with the mathematical calculations needed to make this post possible, can be found here. The second part, which deals with visual approximations of liquid and powder sunscreen, can be found here.]

In addition to the other comments that I have been receiving, a few of you have been asking about spray-on sunscreen. For example, Anna left this comment: "Dude, the spray, the SPRAY! Oh Rob[y]n I totally want to go try out a mass estimate with a spray thing and see what it's really like." Conveniently enough, my scale, spray-on sunscreen can, and poor prioritization skills have saved you the trouble!


I actually use the Coppertone Sport SPF50 every single day for my body because I am fucking impatient as hell. It comes in a 7.5oz can, which is enough for about seven full-body applications if you apply at 2 milligrams per centimeter squared. I paid eight bucks for it at Safeway, so it's about $1.06 per ounce. (I won't calculate yearly costs since you basically always need facial sunscreen, but your geographic location will determine how much sunscreen you need on your body throughout the year. Some of you might wear a parka every day.) This isn't dramatically different from conventional sunscreens. (The Coppertone Sport lotion costs $6.97 for 8 ounces, or $0.87 per oz).

So, how much spray-on sunscreen do you need to cover your body? Measuring spray on sunscreen in a shot glass is kind of meaningless, since you don't "see" it the same way you do with a lotion. Instead, I decided to use time as my measure. Please note that I only tested this one sunscreen and it is perfectly likely that other sunscreens do not dispense product at the same rate.

Using a stopwatch and a scale, I found it took three seconds for my Coppertone Sport SPF50 can to dispense 0.04oz. That means it would take one minute and twenty seconds to get 2 milligrams per centimeter squared application over my whole body. That's a lot of time! This suggests to me that the "added convenience" I thought I was getting from the spray (aka the saved time) is maybe not as significant as I had previously thought, especially since my Coppertone use is making my skin kind of weird and flaky. Based on these results, I think I need to pick up a conventional tube of sunscreen next time I'm at the store. 

That being said, for some people this still may be worth it. Children, especially, are prone to running away when you break out the sunscreen. Chasing after them with the spray-on stuff is usually the safest bet for the squirmy ones.

8 comments:

  1. I like the spray for my body because it doesn't feel so awful, I HATE the way regular sunscreen feels while it's soaking in and I don't usually have a couple of minutes to stand around naked while it soaks in. Plus it makes my clothes stink of sunscreen even after washing which is awful.

    The flip side though is that thanks to avobenzone and our super hard water some of my clothes have orange sunscreen stains. I have yet to find a spray sunscreen without avobenzone :(

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  2. I was wondering what those stains were!
    I love all your posts Robyn- so informative and hilarious. After these sunscreen posts I have found myself leaving sunscreen marks on everything because I apply so much. Reminds me of Tobias and his blue handprints. Ha!

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  3. I used the spray on my kids. It is a lot easier to tell them to close their eyes and spray them down than try to apply tradition lotion.

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    1. I was a preschool teacher for a few years in college and I would NEVER try to use anything but a spray on with those kids! (Plus, at least in this state, if you rub it in, by law you need to wash your hands between each application, which would take forever if you have 20 kids to do. The spray evades that!)

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  4. But isn't there a difference between the level of protection from a chemical sunscreen vs. that of a mineral sunscreen? I've read that one tends to need more of the chemical sunscreen than of the mineral versions? Elta MD makes a nice combo zinc and chemical spray sunscreen.

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    Replies
    1. Not from your perspective as a consumer. It is possible that from the brand's perspective, they need to include less of the active ingredient to get the SPF value they want, but as a consumer the SPF label is ALWAYS at two milligrams per centimeter squared.

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  5. Thank you for the post! I always seem to burn much more easily w/ the spray, even with frequent application (of what seems like tons of the stuff). I'd love to find either a lotion or spray that didn't have that sticky sunscreen feel.

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