Anyone who loves the sun faces a number of dilemmas. How much of which SPF of sunscreen to apply? How much time should you really be out there? And will the sun ever stop moving? (Because moving that chair every hour is a real pain in the neck.)
We can't do much about the sun's positioning — maybe put the chair on a really big turntable? — but math can help you determine just how long you can stay in the sun without burning your skin.
A web-based calculator developed by a physician can determine not only how long you should be in the sun but what SPF of sunscreen you should be using while taking in the rays.
Math fun in the sun
The sunbathing calculator by Omni Calculator — the company makes a number of other online calculators dedicated to equally specific topics — requires you to input a few factors.
"The equation I used to calculate the maximum safe time spent in the sun sounds a bit complicated," Dr. Malgorzata Koperska, who made the calculator, explained to Bustle. "It's the skin phototype coefficient times the cream's SPF, divided by the current UV Index, altitude coefficient and reflecting ground coefficient."
In non-coefficient words, that means you to put in the current sunlight intensity, the altitude of the setting, whether or not you're on water or snow, your skin type and the SPF you're using. Once all that information has been supplied, the calculator displays a value that indicates how long you can stay out in the sun under those conditions, provided you keep applying sunscreen as directed. An advanced option also allows you to input the UV index of your location.
When filling in these values, the trickiest bits will probably be the altitude and your skin type. Altitude defaults at "up to 1,000 m (3,280)" and that should be sufficient for most places, but especially sufficient for beaches. Your skin type, otherwise known as skin phototype, is determined using the Fitzpatrick scale. The explanation of the scale on the calculator site can be a little vague, so poke around elsewhere online to figure out your best match if the categorizations don't make sense for you.
To figure out my particular sunbathing allotment, I input the required values. I live in Tacoma, and summer days tend to either be searingly bright or completely overcast. As I write, it's the latter, but on Saturday, it was the former, and I wanted to evaluate how I well I would've fared on Saturday. So I put in "very sunny" as the sunlight intensity, kept the default altitude and said "no" to being near water or snow. My phototype is probably somewhere between a type III and a type IV — I tanned well when I was younger and rarely burned — so I picked type III just to be on the cautious side, and I use a 70 SPF sunscreen.
According the calculator and those values, I can be in the sun for about 26 hours, provided I kept up on reapplying sunscreen. If I ditched sunscreen entirely on a day like last Saturday, I would have burned in about 40 minutes.
The calculator can also tell you which SPF you should apply. In this instance, you leave the sunscreen field empty and instead tell the calculator how much time you want to spend out in the sun. It'll figure out the SPF you need to meet that goal.
Keeping the sun away
While the calculator could be helpful in maximizing your tanning time while possibly minimizing your risk of a sunburn, it's also not a substitute for medical advice. It also probably shouldn't encourage you to get a tan, either.
Tanning is still the process of exposing your body to harmful UV rays, and a tan is just your body's way of producing more pigment because it's been hurt by those rays. There's no such thing as a healthy tan, according to the Food and Drug Administration. So while getting vitamin D from the sun's rays is good, it shouldn't come at the expense of your skin's health.
I should note that I don't much care for being in the sun, and I don't sunbathe at all. During the aforementioned Saturday, I wore a big floppy sunhat and a loose-fitting, long-sleeved button-down shirt and khakis while I was outside. I applied sunscreen to my face, hands, a patch of my chest and on my arms for when I would roll up the sleeves, just to be safe. In regards to sunscreen, I probably didn't apply enough, because most people don't apply enough sunscreen when they're using it, but the other steps I took were in line with recommendations made by the Centers for Disease Control and Prevention for sun safety.
But if you're going to seek out the sun, be sure to be as safe as possible. Reapply sunscreen, stay hydrated and avoiding being in the sun during peak UV intensity times, typically between 10 a.m. and 4 p.m.