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Important facts about sun light

There are a few facts you need to know about sunlight to better understand its impact on the human body and our environment. Without sunlight no life would have come into being on our planet. It is in many ways essential to our existence on earth. But it can also harm us.

The concept of sun light
If we think of the rainbow, we see light can have different colors, ranging from violet to red. But there is more to light than the colors we are able to see:

Light rays form waves and carry energy. Therefore they can be compared to waves of water. On a calm day the ocean has waves that are far apart. Their wavelength (from one peak to the other) is long and they do not carry much energy. The same with light – some light has long waves and does not carry much energy, other light has short waves, very close together, that carry lots of energy which may be harmful (ultraviolet-light). Just like the ocean waves after a hurricane.

The light we are able to see has a wavelength of 400 to 760 nm (109 meters). Ultraviolet light, also called UV radiation, is classified into three types by its wavelength: UVA ranges from 400 to 320 nm, UVB from 320 to 290 nm, and UVC from 290 to 200 nm. Always keep in mind the shorter the wavelength, the more harmful the energy it carries. Fortunately our earth is surrounded by a defensive shield of gases which absorbs all of the UVC radiation and some of the UVA and UVB radiation. The rest of the UVA and UVB light, which passes through no matter if it is cloudy or sunny, can have different impacts on our skin.

The impact on our skin
Through UV exposure our DNA in the cells of our skin is damaged. Either those damaged cells die or they get repaired by the cell´s own repair mechanism. But if the damage is too severe and the cells cannot regenerate, those damaged cells can turn into skin cancer.

UVB radiation
UVB is known to be responsible for the long lasting tan one possibly gets when staying in the sun. It is the main factor in causing sunburn and skin cancer. Although it does not penetrate into the skin as deep as UVA it carries lots of energy. That is why the first sunscreens included a UVB filter.

UVA radiation
Until today, scientists thought that only UVB was responsible for causing skin cancer but they had to realize that 10 to 100 times more UVA (compared to UVB) reaches the earth. In high doses, it caused skin cancer in animal experiments. They also had to realize that although it has less energy, UVA radiation penetrates deeper into human skin than UVB. It is also the main cause of skin aging. So there are enough reasons why you should always wear a sunscreen that protects you from UVA and UVB (so-called broad spectrum sunscreens). Uni Heidelberg