SUNSHINE, CAN BE USEFUL OR HARMFUL TO HUMAN

When we live in big cities, where there are so many skycrapers limit sunlight reach our bodies, we agree that how valuable is the sun for our living. People from those cities spend their vacation time to go to the places where there are a lot of open sunlight. Beaches in tropical countries is their main destination. However, the sunlight can be harmful if we are exposed too long in the open field. The article below perhaps is valuable to read for whom loving going to open field in tropical countries.

SUNSCREENS
by Lynn_Willis
 
Without the sun, there would be no life on Earth. It keeps our planet warm. Plants need the sun's radiant energy for photosynthesis. People need small amounts of exposure to activate vitamin D in their bodies, a substance important to bone-building and other biological processes.

You can have too much of a good thing though. Too much sun can cause sunburn. Over time, too much sun can age the skin, making it leathery and inelastic. Researchers have also noticed a strong correlation between too much sun when you are young and skin cancer when you are older.

Sunlight is made of many different kinds of light. These kinds of light have different energies and their properties are a result of these energies. Not all kinds of light cause sunburn. Only ultraviolet (UV) light damages skin.

Light energy is measured in wavelengths?the smaller the wavelength, the greater the energy. UV light is usually broken down into three subtypes:

UVA, 320 >> 400 nm wavelength 
UVB, 290 >> 320 nm wavelength 
UVC, 200 >> 290 nm wavelength 

UVC light will do the most damage to your skin. Fortunately, this kind of light is completely absorbed by the atmosphere. Too much UVB light is responsible for sunburns. UVA light can damage your eyes over time. UVB and UVA go right through the air and clouds, which is why you can still get sunburned on a overcast day.

Sunscreens work by absorbing some of the UV light before it reaches your skin. Compounds such as cinnimate, oxybenzone, salicylates, and dibenzoylmethanes absorb UV light at different wavelengths, so many manufacturers put more than one UV-absorbing compound in their spray or lotion to give better protection from the sun. Most sunscreens block UVB rays.

Scientists aren't sure which type of UV light "UVA or UVB" causes the increased likelihood of skin cancer. To be sure you are protecting yourself from damaging rays, sunscreen should be one part of an overall strategy to keep your skin healthy. In Australia, the country that has the highest rates of skin cancer in the world, people are urged to "slip, slop, slap". That is, slip on a shirt, slop on sunscreen, and slap on a hat when you need to spend time in the sun. Staying out of the sun during peak hours (10 a.m. to 4 p.m.) is also recommended.
 
original source: www.chemistry.org