Warm sun on your skin is a boost to the spirit, and we all love a summer's day in the park or at the beach. But too much of it can cause a lot of pain.
Sunburn starts with the sun's ultraviolet radiation bombarding the cells in our skin. UV rays carry about 40 times more energy than visible light and penetrate human skin faster. With this much energy they can easily damage skin cell DNA.
When our skin is exposed to UV rays, it triggers special cells that start pumping out melanin - the pigment that gives our skin colour.
If the exposure is show and gradual, melanin spreads around skin cells to form a protective layer that we recognise as a tan. But if it's rapid and intense, UV rays can penetrate skin cells and start destroying their DNA is as little as 10 minutes.
Then around six hours later blood begins to seep into the burnt areas to heel these damages cells. This causes inflammation - and that's the pain and redness we all associate with sunburn.
Within two days the skin starts to peel away as new cells push out those dead ones. In fact, common neck and back sunburn can lead to the shedding of more than 25 billion skin cells - that's about 250,000 times more than the number of hairs on your head.
And don't be fooled, you can still get sunburn on cloudy and cooler days. That's because up to 80 per cent of UV rays can pass through thinner clouds.
Also, make sure you're particularly careful at the beach. Sand and ocean water can act like mirrors and reflect about 15 per cent of UV rays right back at you and make your sunburn even more painful.