The sun emits UV rays (ultra violet) in the following lengths:
The Earth's ozone layer is a low-density band of ozone (o3 or Trioxygen) in the stratosphere, which is 10-50 km above the earth's surface. The ozone filters out all the UVC light and most of the UV-B light, and none of the UVA light. This means that 98.7% of all UV radiation that reaches the earth's land and water surfaces are UVA light rays.
UV rays are invisible to the human eye, as rays of energy coming from the sun. If not sufficiently protected while being exposed, or overexposed, these rays can cause considerable burn damage to our eyes, hair, and skin.
UV rays can cause chemical changes in the body that suppress the body's immune system and stimulate the growth of cancer cells by generating toxic substances known as free radicals. These substances, which attack and damage our DNA, contribute towards skin cancer. However, there are certain molecules in vitamin-rich foods, or anti-oxidants, that absorb these free radicals and prevent any further damage.
The following chart illustrates the different type of rays from the sun and more specifically the different UV light rays.
The sun provides wonderful life-giving energy as well and it is very important to understand the extent of the UV rays' role in our overall functioning. Of increasing importance the more we learn about it, is the fact that UVB rays assist our bodies in making Vitamin D, which strengthens our bones and teeth and assists our bodies in building immunities to such diseases as Rickets and colon cancer. Limited exposure to UVB rays is encouraged for those who are Vitamin D lacking.
UV rays are also used to treat Psoriasis. By exposing the affected skin to UV rays, it will slow the growth of the skin cells, preventing an outbreak of the itchy patches for which psoriasis is known. In addition to this, these rays have various commercial uses including sterilization and disinfection.
The animal and plant kingdom seem to use ultra violet rays for a multitude of purposes, many of which we haven't begun to understand. Eg. Plants photosynthesize and some animals appear to have the ability to see ultra violet rays and UV vision helps bees to collect pollen from flowers.
However, one thing everyone is agreed on is that too much exposure has the ability to cause sunburn. If the skin absorbs too much of the sun's energy from the UV rays, it turns red, hot, may sting on contact and feel generally very uncomfortable. Essentially, sunburnt skin alerts our blood to rush to the sunburnt area to cool the damaged skin, after which the damaged, dead skin will be able to peel away. This may have caused DNA damage that in turn leads to skin cancer.
Darker skinned people may not burn however, but are equally as susceptible as fairer skinned people's skin is to the damage caused by over exposure to the UV rays. So you don't necessarily have to had a sunburn to start the process that ends up in skin cancer!
Ultra violet ray damage caused to eyes is initially a pain or temporary blindness and blurred vision. Over time, however, ultra violet ray damage will ultimately result in the growth of cataracts on the eyes.
Physical protection is advocated as the best way to start to deal with ultra violet rays. EG: physical barriers such as wide rimmed hats, Hats with flaps down the back of the neck, long sleeved shirts, trousers or long robes instead of shorts, all defend the body. UV protective sunglasses also help to protect the eyes. What many people don't think of is their hair. Just by wearing a hat, you protect your hair from UV damage.
Besides clothing, the next best option is a sunscreen with a physical block as an ingredient. Besides the SPF rating, the important thing to look for is a physical block ingredient - either zinc oxide or titanium dioxide as these will provide for protection from both UVA and UVB rays. A good habit, especially if fair skinned, is to wear a sunscreen every day you are going to be exposed to the sun. If anticipating long exposure, cover up, use sunscreen and enjoy the sunshine for all it's positive benefits!