How does sunburn work

I’ve never quite worked this out. Let’s say, to use convenient figures, that it takes fifteen minutes for me to burn in the sun. If I go outside for ten minutes, inside for ten minutes and then back outside again have I got another fifteen minutes left until I burn? What if I go inside for an hour? What if I alternate every five minutes?

I don’t think it’s linear and it clearly isn’t cumulative because if I wait overnight then it seems to reset. Any ideas?

It “resets” overnight via a process called “healing” and another one called “tanning”, which provides future protection to your skin.

You are clearly only talking about minor sunburn, because more serious burns do not “reset” overnight, they take longer to heal.

If it “resets” overnight then why not after two or three hours during the day?

Because it takes time for your cellular structure to repair radiation burns.

You start burning the instant you go out. You start repairing shortly thereafter. Some people repair sun damage faster than others – they can stay out longer, and can go back out after a shorter duration indoor “dark repair time.” And they tan better, so they can extend their sun exposure.

Fun fact: the oxidative processes in every cell that keep you alive also generate free radicals, that damage every cellular component. You are constantly being destroyed from within even as you live, and constantly repairing the damage. You become less efficient at repair as you age. Until you die.

You can stop worrying at that point. Or sooner depending on your mental fortitude.

Sunburn is your body being physically damaged by radiation. Technically what is happening is that

  1. Ultraviolet radiation hits your skin
  2. Your DNA is drectly damaged by it
  3. Your body reacts to this with an immune response

It’s NOT the heat that causes it. Its the UV. This is why it’s extremely hard to get sunburn in a car through the car’s windows, even if it’s hot; a car’s glass is not transparent to most UV.

Every visible and tactile symptom of sunburn - even the fatigue and dizziness it can cause - is a result of your body’s immune response.

The extent of your reaction to it is therefore a function of the amount of damage and relative tendency of your body to respond to it. The reason you feel you “reset” overnight is because for most people, 8-10 hours is enough for the body to complete its reaction to a mild sunburn and then for the immune response to stop. For a shorter period out of the sun - or a much worse sunburn - your body will still be reacting to the first burn when you step back into the sun and so the burn will rapidly worsen.

Five minute breaks because short exposures will probably make no difference at all. If your skin will burn in 30 minutes of exposure, breaking that up over an hour of time will make very little difference, because your skin is still absorbing a damaging amount of UV in less time than your body can muster an effective response to the DNA damage. Much longer breaks would work though - say, 30-minutes breaks between 5/10 minute exposures.

yes, but in the sunburn context you could say that the UV rays produces a high enough level to cause cell death. So that the non-dead ones are undamaged. They don’t have to do much, just hang around long enough to hold the skin together, so that new skin can grow properly…

The cells probably can’t reduce the levels, they just die with a medium level, and so it will take days for significant replacement of the skin cells to say that the sun’s effects have gone.

So if you get a slight burn, you will burn quickly the next day, as many of the cells that could die from UV would still be high in the toxins that will kill it.

In terms of damage, such as DNA , skin cancer, collagen and wrinkles, perhaps different. this is only about the literal sunburn not the long term consequences. However, the same free radical attack that kills cells may also prevent DNA repair in those medium poisoned cells. For some reason, sunburn wipes out collagen… perhaps the fast growing replacement skin … needed to repair a sunburn… doesn’t have time to produce as much collagen, and then its collagen reduced for ever after.

Wow, thanks for the great responses.

I can confirm this.

Some years ago I was doing some TIG welding[sup][/sup], and performed a series of tack-welds[sup][/sup] without lowering my helmet. Each tack-welding event lasts for only a fraction of a second; one tack-weld wouldn’t have been a problem, but this was several dozen in a row, and it blasted my face with a lot of UV. I never felt any heat from it, but I developed an extremely severe sunburn on my lower face. It’s definitely the UV, not the heat.
[sup]*[/sup]TIG welding: this is a welding process that uses argon gas to shield the electrode and weld metal from oxidation. It produces very little smoke (compared to, say, stick welding), and therefore allows a lot of UV radiation to escape to the surrounding area. My situation was further exacerbated by my welding table, made of bare metal that reflected plenty of UV back up toward my face. :smack:

[sup]*[/sup]Tack-welding: instead of clamping parts together before the main welding event, you hold them in place with one hand and use your other hand to create one or two very quick, tiny welds that temporarily lock the part in place. In the days before auto-darkening helmets, you needed to leave your helmet up while positioning your parts - and then of course you’d leave it up and just briefly close your eyes while you did the tack-weld. After burning my face, I went out and immediately bought an auto-darkening helmet. :smack: