If you have been inside all winter and then go sit out in the sun on a bright spring day, it is very easy to get sunburned. Over the course of several hours, exposed skin turns bright red and becomes extremely painful when touched. The skin will often feel very warm as well.

When you get a sunburn, you're basically killing skin cells.

The outer layer of skin on your body is called the epidermis. The outermost cells of the epidermis -- the cells you see and feel on your arm, for example -- are dead. But just below the dead cells is a layer of living cells. These living cells continuously produce new dead cells to replenish your skin.

By sitting in the sun, you expose yourself to ultraviolet light. Ultraviolet light has the ability to kill cells (see this page for details). Ultraviolet light hits the layer of living cells in the epidermis and starts damaging and killing them.

As your body senses the dead cells, two things happen:

  • Your immune system comes in to clean up the mess. It increases blood flow in the affected areas, opening up capillary walls so that white blood cells can come in and remove the damaged cells. The increased blood flow makes your skin warm and red.
  • The nerve endings for pain begin sending signals to your brain. If you have read How Aspirin Works, you know that damaged cells release chemicals that activate pain receptors. This is why sunburned skin is so sensitive.
The ways to avoid sunburn (without having to stay inside) are to use a sunscreen, which blocks ultraviolet light, or pace yourself so you get a tan first. When you get a tan, your body essentially creates its own sunscreen using special pigment cells in the epidermis. See How Sunburns and Sun Tans Work for details.

Here are some interesting links: