The period while embryo is taking form is an essential process in human’s growth. The embryo is very sensitive to the womb’s environment as such that any damages during this period can have irreparable effects on it. Teratogen is a name given for damaging factors to the embryo during the pregnancy. Generally, Teratogen Include environmental and mother-related factors. However, the precise analysis of different materials around us and research about whether they are Teratogen is too much to fit in this article and it certainly needs more research in future. However, in this article there is an attempt to identify the most important and Well-Known Teratogen during the growth of embryo and some of the detected damages. Legal drugs such as Teratogen anti epilepsy and illegal drugs such as heroin, Teratogen Marijuana, etc., including cigarettes, alcohol, radiation, environmental pollution such as mercury and its derivatives, copper, chloride copper, etc., are some of the examples of environmental Teratogen and diseases such as rubella, herpes and HIV viruses, malnutrition, weaving, blood Rh agreement, age, mother and birth related Teratogen will be discussed in this article. Awareness of Teratogen detecting their harmful effects and also the prevention can lead to the reduction in the birth of exceptional children.