UVA, UVB, infrared: here's the lowdown on sunlight!

The solar spectrum consists of electromagnetic energy rays that, to some extent or another, penetrate the skin, inducing both beneficial and harmful biological effects. We are constantly being bombarded by varying levels of ultraviolet (UV) light, as well as other solar rays, infrared rays and so forth... UV rays are ultraviolet radiation emitted by the sun. There are three types: UVA, UVB and the lesser known UVC. Whatever the weather, UV rays are omnipresent in the atmosphere and it's between midday and 4pm that they are at their strongest: you can avoid exposing your skin during this part of the day or apply a suitable sunscreen to protect bare skin. UVC rays are the most harmful and the shortest. They do not reach the surface of the earth, as they are filtered out by the atmosphere and blocked by the ozone layer.

UVA rays have a relatively long wavelength, meaning 95% of UVA radiation reaches the earth's surface. Present all year round, even on gloomy days, they penetrate clouds, glass and the epidermis. Although painless, they can penetrate the deeper layers of the skin, to reach the heart of the dermis cells. UVA can damage cell's DNA, cause sunburn, inflammation, sun allergies and pigment problems. It's also the primary culprit when it comes to ageing skin: it weakens collagen network loosens the skin, reduces firmness and causes wrinkles.  

UVB rays, which have a medium wave length, do not penetrate beyond the superficial layers of the skin. Their intensity varies throughout the day, peaking at noon, although they are blocked by cloud cover. UVB rays have an effect on the epidermis: they stimulate melanin production, which darkens the skin and protects it from sunlight. Within 48 hours, these ultraviolet rays cause the appearance of a lasting tan. But they are also responsible for sunburn, as well as allergic reactions and skin cancers.