What is a sunburn?

Cynthia Bailey, MD|June 20, 2011

A sunburn tells you that damage and inflammation have happened inside your skin from UV exposure; you exposed yourself to more sun than your skin type can handle.....and there's simply no good news about it! Understanding why a sunburn happens can help you figure out what steps you need to take so that you can have all the fun you want outdoors without getting burned. If, heaven forbid, you do get a sunburn, then knowing how to take care of your inflamed skin will help you heal faster. In this Sunburn Series I’m going to give you a dermatologist's explanation of what happens in your skin when you get

  • a sunburn (i.e. why it's red and hurts)
  • a tan (i.e. how much sun protection you get from one)

I'm also going to give you some helpful information to heal sunburned skin and explain how to prevent ever getting a sunburn again. Your skin type determines how much sun your skin can take. Obviously, the fairer your skin, the less sun you’re designed to tolerate (i.e. your ancestors lived in places with very weak sun and cooler temperatures, and were often covered in layers of clothing).  You can't change this.  Fair skinned people will sunburn faster than people with olive or brown skin.  But remember, every skin type can sunburn.

What causes a sunburn?

The answer is all about wavelengths of ultraviolet light and what they do to your skin. UVB Rays UVB rays are the major cause of a sunburn that comes from the sun. The SPF on your sunscreen product describes its protection against these UVB rays.  UVB ray intensity varies during the year and according to where you are in the world.  This means that you need to know when the UVB rays are most intense to understand your sunburn risk. UVB rays are most intense

  • during the middle of the day between 10 am and 3pm
  • in the summer
  • the closer you are to the equator
  • when they are reflecting off things like sand and snow (sand and snow reflect up to 85% of UVB making for really intense exposure)

Clouds don’t really block much of the UVB rays and they penetrate into water too. UVA Rays UVA ray intensity does not vary like UVB.  UVA rays are out all day, all year, everywhere in the world.  They are reflected off sand and snow and penetrate into water. There are a lot more UVA rays from the sun than there are UVB rays, but they still don't cause most of your sunburn.  This is because the UVB rays have a special efficiency at causing skin redness and so you burn first from UVB and get out of the sun before the UVA rays can burn you too! Anyone who has seen someone with a tanning bed burn, however, knows that UVA (the rays that are in a tanning bed) are capable of burning skin. In a tanning bed the UVA burns skin because there is no UVB to burn you first.  This means that in a tanning bed you're getting a lot of UVA, and this isn't good either.  UVA penetrates skin more deeply than UVB making it especially powerful at causing wrinkling and damage to the deep layers of your skin.  It's why I thing the damage of tanning bed exposed skin looks different over time than sun exposed skin.  On a skin exam, I see more freckling, wrinkling and widespread skin thinning.  The tan is different too, which I'll explain in the next post.

What is a sunburn?

It’s actually a normal reaction from overexposure to UV rays.  A sunburn happens when an inflammatory cascade of events begins in the skin from the excessive UV exposure.  Some of the cells of your skin actually die, called 'sunburn cells'.  The process involves:

  1. Redness, which usually starts to show up 6 hours after excessive UVB exposure.  It peaks  about 12-24 hours later.  It can show up faster and be more severe in extreme sun exposure (i.e. really fair skin on a tropical beach)
  2. Tenderness, which follows the redness.
  3. Blistering happens after extreme exposure.
  4. Peeling usually occurs in a week, regardless of whether there was blistering.
  5. Really severe exposure will also cause skin swelling (edema), fever, chills, nausea, rapid heart rate and even dangerously low blood pressure.  This can last up to a week and can be a medical emergency.

A sunburn is like a sickness or poisoning.  Nothing good comes of it. When the skin is red and inflamed it's weak and requires special care, which I'll describe in the 3rd post in this series titled How To Treat A Sunburn.  Following a sunburn the skin heals but is forever damaged.  The more frequent and severe the burns, the more damage.  In the worst case this means an increased risk for melanoma (the 'big C' skin cancer).  It also means permanent sunburn freckles, skin thinning and increased risk for all skin cancers.  A sunburn isn't just a trivial inconvenience or a necessary path to a tan, it's a problem to be avoided. In the second post in this Sunburn Series, I explain what a tan really is inside your skin, and how much sun protection a tan gives you.  Click here to read What Is A Tan?

Don't want a sunburn and have plans to be out in the sun?  Need trustworthy dermatologist quality sunscreen and sun protection asap?  I don't want you to burn either - my patients know that seeing sunburned skin always worries me!  Click here for my:

Sun Protection Kit

Sun Protection Hats

Reference: Andrews' Diseases of The Skin, 11th Edition, William D. James, MD, Timothy Berger, MD and Dirk MD Elston, MD, Saunders 2011, pages 24-25. Photo: Thanks and gratitude to Alan Donque and Kirin Queen

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