The Solar Spectrum

The ozone, clouds and air pollution partly absorb radiation emitted by the sun.  Different parts of the solar spectrum reach the earth in various ways:  some directly and some indirectly after being scattered in the layers of the earth’s atmosphere.  The scattering depends upon the wavelength:  the shorter the wavelength, the greater the scattering.  Luckily, the sun’s most damaging rays, UVC never reach the earth’s surface.  Invisible UVA & UVB rays damage skin most. 

UVA rays penetrate into the connective tissue and are the primary cause of chronic light-induced damage, such as premature skin aging. They are also responsible for the formation of free radicals and for phototoxic, as well as photo allergic reactions. 

• Polymorphous Light Eruption (PLE) is the most common sun-induced skin disease.  The formation of free radicals through UV radiation is considered one of the causes of the disease, which occurs mostly in young women. 
• Photo allergic and phototoxic skin reactions may be triggered by chemical substances including certain active ingredients of sunscreen and skincare products exposed to sunlight or by taking certain medicines during sun exposure. 
• Free radicals, highly reactive chemical compounds with free electrons, damage the cells of the epidermis and dermis.  UV radiation triggers their formation, which over years, leads to signs of chronic light-induced damage. 

UVB rays penetrate into the deepest cell layers of the epidermis and are the main cause of sunburn, DNA-damage and the development of skin cancer. Warming infrared rays and the rays of visible light play no role in these effects.