The first-ever international study into the effects of passive smoking has found it causes six hundred thousand deaths every year across the globe. The study by the World Health Organisation analysed data from nearly 200 countries and found that passive smoking is particularly dangerous for children who are exposed to it in their homes.The WHO says, about a billion people smoke every year and five million of them die from smoking-related diseases like cancer, heart disease and other respiratory illnesses. The WHO says, tobacco is now the biggest public health threat the world has ever faced and urgent action is needed to protect children from the dangers of second-hand smoke. The study reveals that 40 of world's children regularly breathe air polluted by tobacco smoke which can cause asthma, phenomena or sudden instant death syndrome.