Smoking
Enough publicity has been given to the adverse effects of tobacco smoking on health. Smoking not only causes cancer and heart diseases, it is also a very common cause for several serious lung diseases. Passive smoking is as bad as active smoking. Most people with asthma are sensitive to smoke. This is because the lungs affected by asthma tend to overreact when the smoke stimulates sensitive receptors in the airways. These receptors carry messages that make the muscles around the respiratory passages contract. The airways therefore become narrow and cause symptoms of asthma.Smoking during pregnancy is especially dangerous. Babies born to mothers who smoked during pregnancy have nicotine levels as high as those in adult smokers. They are also more likely to develop respiratory diseases including asthma during early childhood.