Go into the sun unprotected in any way and UV rays (both UVA and UVB) immediately penetrate your skin.
What happens in the skin cells?
Step1: The UVA and UVB rays penetrate the clouds, thick layers of glass, a metre of water, and the layers of the skin.
Step 2: The UV rays act like chain saws, shredding the DNA (the genetic material, with a very precise structure, very specific order and very specific coding) of the cell nuclei.
Step 3: Repair enzymes in the cell try to repair the damage to the DNA chain as quickly as possible. This damage and repair happens all the time, and the tempo of repair can keep up with a certain amount of damage. The repair enzymes can get tired or just not be enough.
Step 4: When the damage is excessive (and this can be even before your skin turns red), the enzymes cannot cope. The result is a scrambled DNA structure and scrambled coding, which leads to normal cells going haywire (mutate). This is the first step of the formation of cancer cells.
Step 5: UV-rays also encourage extremely toxic superoxides to accumulate in the cells.
Step 6: These superoxides speed up cell ageing.
Step 7: It appears that selenium prevents the build-up of superoxides, and that anti-oxidants such as vitamins A, E and C may also protect the DNA.
Step 8: Benign freckles and sunspots may need just one extra exposure to sun to become malignant.
Can you see the damage?
UVB causes the top layers of your skin to release chemicals that make your blood vessels expand and leak fluid, causing pain, inflammation and redness – it’s known as sunburn. This sort of damage can happen within as little as 15 minutes and can continue to develop for up to 72 hours after you’ve been exposed to the sun. The skin cells damaged by this will die and peel away in flakes or sheets. Peeling is your body's way of disposing of dead skin cells.
UVA penetrates into the very deep layers of the skin, affecting the living skin cells that lie under your skin's surface. It’s these rays that bring about longer-term damage such as wrinkles, sagging and discolouration. It also lays the groundwork for skin cancer in the future.
Which is best/worse - one serious case of sunburn or long, regular exposure?
People who have had three or more serious cases of sunburn before the age of twenty and weekend sunbathers who want an instant tan have a greater risk of melanoma. Farmers, cricketers, golf players and others who have long, regular exposure to the sun, have a greater risk of milder skin cancers.