Ultra violet radiation is a form of energy emitted from the sun. On the electromagnetic scale, it is in between visible light and x-ray radiation.
UVA rays have the longest wavelength of UV rays and are able to penetrate deeper into the skin than other UV rays. UVA rays are responsible for the immediate tanning effect and photoaging inclusive of pigmentation, collagen and elastin destruction.They are also able to penetrate through clouds and glass. You can protect your skin from UVA rays by using a broad spectrum or mineral-based sunscreen.
UVB rays have a shorter wavelength than UVA rays and therefore can only reach the top layer of skin (the epidermis). UVB rays are responsible for the delayed tanning effect and sunburn. They are at their strongest in the UK from May through to September between the hours of 10 am and 2 pm.