[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!
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).
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.