The sun provides light, heat and ultraviolet radiation (UV radiation). UV radiation can be divided into three groups, UVA, UVB and UVC, depending on the wavelength the radiation has. The energy in the radiation depends on the wavelength and a shorter wavelength means a more energy-rich radiation. A slightly simplified picture of how the radiation affects us is that the more energy the radiation is, the greater the risk of damage.
UVA radiation is the radiation that is the least energy source. From the sun and from solariums, the bulk of UVA radiation is the UVA. Solaries also usually have a higher proportion of UVA radiation than the natural sun. UVA makes the pigment in the skin dark. UVA penetrates the deeper layer of the skin. It causes the skin to age early and can cause skin cancer. UVA radiation can also break down vitamin D in the skin.
UVB has wavelengths that are shorter than UVA radiation and therefore more energy energy. The ozone layer in the atmosphere filters out large amounts of the harmful part of the UV radiation and limits the amount of UVB radiation that reaches the ground. It is mainly UVB radiation that causes us to burn if we solar too much. It also causes skin aging and can cause skin cancer. UVB does not penetrate as far down the skin as UVA does.
UVC radiation is very energy-rich. The sun’s UVC radiation does not reach the ground because all UVCs are absorbed by the atmosphere. UVC radiation is used, for example, in special lamps to kill bacteria. The sensitivity to solar radiation is due inter alia to on what skin type you have. There are six different skin types with different sensitivity to solar radiation. The lower the number, the more reason to be careful. Skin type 1 should always protect itself while skin type 4-6 (brown to dark brown skin color) does not need to be as careful.