Depending on the length of radiation UV radiation is divided in 3 parts:


UV-A (very short waves)
UV-B (short waves)
UV-C (long waves)

UV-C radiation:
is absorbed completely by the atmosphere through oxygen and ozone.
 
UV-B radiation:
less effective, the Ozone Layer absorbs up to 90 %.
UV-B is responsible for sunburns.
 
UV-A radiation:
is absorbed only in small quantities by the atmosphere.
UV-A radiation makes the skin older.