Ozone layer or shield is present in stratosphere which is also called ozonosphere. It lies at an altitude of 23−25km over equator and its concentration is 300 dobsons. It functions as a shield against strong UV radiations. Protection from UV radiations is proportional to thickness of ozone layer. Depletion in the concentration of ozone is called ozone hole. Thinning of ozone layer increases the amount of UV-B radiations reaching the earth. It would increase occurence of cataract, skin cancers, herpes, dimming of eye sight, photoburning, deficient functioning of immune system.