How To Avoid Sunburn Without Sunscreen

Core Tenets

From the attached studies we can propose the following theory:

• Skin temperature rises predictably during exposure to the sun, quickly reaching a threshold temperature around 104° at which it will halt, until the preparedness of the skin is surpassed, whereupon skin will raise an additional 2°+, when burn is either imminent or occuring.
• Relatively short periods in the shade can allow skin to return back to its usual cooler temperature around 98°, and this return marks genuine replenishment of distance from sunburn.
• Sunburned skin, before it has shown any other reliable signs, will first exhibit a much slower return to 98°, or even stay above 100° until after it has gone red and then healed.
• The tanness of skin is a comprehensive marker of its preparedness for a given quantity of sun exposure. Tan skin will heat up slightly slower, be less likely to heat up to the threshold temperature, and if it does, can withstand staying at the threshold temperature for longer durations of time without breaching or approaching sunburn.
• Angle of skin exposed to the sun is highly relevant: directly perpendicular skin is most powerfully affected. Skin at a 45° off from perpendicular to the sun, of the same tanness as skin 0° off (i.e. directly perpendicular), will burn before the latter.
• Low angle sun is weaker. The sun peaks at 12-2 depending on your region and daylight savings time. (You can find your location's time for the zenith using the Dminder app). The UV during the peak of the sun's arc is strongest, and most useful for preparing one's skin for the worst case scenario.
• The UV scale is linear, and direct, meaning a UV of 12 is very much 'twice the strength' of a UV 6. Skin trained at a UV 6 should be expected to be essentially untrained for a UV 12. Caution should be used whenever skin is exposed to UV 2 or more levels higher than previously adapted to.
• Some body areas with less volume will naturally shunt heat better and will less tightly demonstrate the above rubric, namely lower forearms, ankles, etc.

Since tan skin is capable of practically arbitrary sun exposure within the plausible habits or occassions of modern life, safety from sun induced damage is effectively secured by the attainment of skin tanness commensurate with the maximum UV strength of the sun in one's region, at the given season.

Core Steps

The only challenge left to navigate, then, is the process of achieving this level of tanness without falling prey to accidental sunburns. After much testing I have devised the following process, which has worked for me as a "Fitzpatrick Type I" (read mockingly) pale redhead. It is designed specifially for this transitory phase, when highly unprepared skin is being exposed to a new level of UV, and adaptation (tannning) is desired. It is as follows:

1. To start, you presuambly are least tan, of the areas you are looking to protect from sun exposure, on your chest. This means that your chest can act as a 'canary in the coal mine': it will be your reference area. The palest area will be the first to burn, meaning that if we focus narrowly on protecting it, it will result in prevention of sunburn anywhere else. By using the stomach, we also choose a highly reliable area [see (h) above].
2. Find a location in which you can lay down fully in the sun, preferably at one angle. [If you raise up the back of the chair you can introduce a difference in angle to the sun which may leave inadvertently more direct zones vulnerable to sunburn, see (e)]
3. If at all possible, I highly recommend making shade immediately available, such as a second seating arrangement just feet away, fully in the shade. The idea is to be somewhat capable of relaxing during this process, but you want to make sure that laziness does not trick you into offputting the switch into shade. (When skin tanness is much closer to the intensity of the sun in question, flipping between prone and supine is a perfectly valid way of introducing shade.)
4. Your hands (depending on your salt deficiency, and region) may need a few minutes outside to warm up. Allow a minute or two for your hands to reach a similar temperature as the rest of your body.
5. Check by feeling your reference area with your hand, especially the with the crease between palm and fingers. Get used to what this feels like during shade (after acclimating to outside temperatures).
6. Lie down in the sun, ensuring your reference zone is the most direct to the sun, and after a dozen seconds or so, check with your hand. See if you can feel any difference. You probably won't yet: Over the span of the first 60 seconds if strong UV for your tanness, 120 if less so, you should be able to detect the rise in temperature to the threshold. The threshold should not feel painful or worrying, just toasty*.
7. Relax. The sun is not an evil death ray. You are receiving a very complex and ancient stimulus, which every cell in your body is expecting to occur. The pale green sludge, out of which life first emerged in the known universe, did so very much right beneath daily sun's rays, and every single evolved, land-faring descendent since then has dealt with the same.
8. Now, remember that you've been a deranged moderner for a long time, and your skin is being exposed to novel UV. Check with your hand your reference zone. Does it feel the same as the threshold temperature? This check should take about 3 seconds, feeling multiple areas, and being quick so as to not unduly provide checked portions of the skin's surface bouts of shade. Is it simply very warm? If so, continue as you were, waiting around 60 seconds in strong UV for your skin, or 3 minutes for weaker UV.
9. There will come a point when the feeling crosses over from "very warm" to "quite hot," from "sunbathing cat" to "likes their showers to hurt"*. Specifically, I find that my pain receptors begin kicking in right around 105°/106°. If there's pain, this is the threshold being breached, and skin heating up to 104°-107°. That's a fairly big range, and if you're catching it early, the sun's not more than 1-2 UV above your level of adaptation, and it's only 104°, there's nothing wrong with lingering about a minute or two. If you're quite pale/unadapted, you'll find that 104° is only a few dozen seconds away from 106°, and you should not risk lingering much at this stage.
10. After you're done lingering or not lingering, return to the shade. Allow your skin to return to its baseline around 98°, and give it a minute thereafter. This should total to around under 5 minutes. (If it takes much longer than that, stop for the day)
11. So far as I can tell, this is repeatable indefinitely. In practice, however, if you are being exposed to UV strong for your tanness, the time it takes to breach threshold will progressively lessen across bouts of sun. If this length becomes as short as 30 seconds, you've certainly done enough, and shouldn't risk accumulating a burn out of many slight exposures to higher temperatures — it becomes too impractical at this point to keep aloof from excessive accumulated time spent above threshold.

*Keep in mind, that I have no way of knowing without the report of others whether the thresholds and signposts I have described are found in at the same levels for other people. I am confident that the general story still applies, but the exact proprioceptive and tactile signatures that I am using for myself may turn out to be poorly calibrated for someone with, say, a higher pain tolerance than redheads, for whom using the above metric could then result in sunburn. We do not know.

With the use of successive 1-hour sessions following these rules, I have tanned arbitrarily much. I have moved from Pacific Northwest's UV 6 summers to Georgia's UV 12 summer, without more than a single slight burn on the shoulders, which was the original discovery of (e).

Once you've adapted to the sun in your region, keeping in mind that you may need some upright-standing exposure for the top of your shoulders, according to (d), you will be capable of engaging in whatever outings you want, without sunscreen or worry of burn.

Finding Yourself Unprepared

When choosing to go without sunscreen on one of these outings, it pays to be cognizant of the implications of this theory for how you ought to behave under circumstances where you find yourself insufficiently prepared for the sun to come. Turning to sunscreen is rarely preferrable, if ever. The following tips can help ensure you do not burn in such an occasion:

• Seek shade in your path early. It's better to nurse pale skin with constant shade, than to find yourself with pale skin reaching threshold and subsequently direly needing repeated shade. If you know the situation will involve targeted areas being exposed, start shade breaks early.
• Bring a towel, small or large, or just use a shirt, for portable, adjustable shade. In contrast to tanning, most outdoor activities actually occur upright, meaning due to (e) that your most intensely vulnerable areas are just your shoulders (or maybe your ears if you really need to get outside more). Periodically spending short periods covering in this way can provide relief during kayaking or hiking.
• Turning to face a different side of your body to the sun effectively engenders shade to the opposite side. This, again, needs only be done in small bursts.