It's a little more complicated than a simple heat-and-char process. Immediately after sun exposure, you'll see some pink skin: That comes from dilation of the capillaries in reaction to ultraviolet B rays.
"The actual burn you see later comes from a series of chemical reactions," says Mehmet C. Oz, MD. Mast cells in the skin release chemicals like histamine and serotonin, triggering more chemical production and inflammation. Within 12 hours, skin cells begin to die, and inflammation turns the skin a darker red.UV radiation damages your DNA, setting you up for possible skin cancer and suppressing immunity. But your skin does try to fight back. As soon as you're exposed to UV radiation, cells called melanocytes release melanin pigment that blocks UV rays-in the form of a tan that can reflect UV light. You've heard it before, but it bears repeating: To prevent burns, use a sunscreen that blocks both UVA and UVB rays, and reapply often.