What are teratogens? How they are dangerous to the unborn child?

Teratogens are environmental agents that cause deviation in normal development in an unborn child and that can lead to serious abnormalities or death. Common teratogens include drugs; infections, radiations and pollution. Intake of drugs (marijuana, heroin, cocaine, etc.), alcohol, tobacco, etc. by women during pregnancy may have harmful effects on the foetus and increase the frequency of congenital abnormalities radiations (such as X-rays), and certain chemicals near industrial areas can cause permanent changes in the genes. Environmental pollutants and toxic wastes like carbon monoxide, mercury and lead are also sources of danger to the unborn child.