An agent that can cause malformations of an embryo or fetus. This can be a chemical substance, a virus or ionizing radiation. This is closely related to a fetotoxin, an agent that causes poisoning effects on a developing fetus. Both fetotoxins and teratogens are reproductive toxins, substances which cause damage to one's reproductive and/or endocrine system and/or a developing fetus. Additional Info: Pregnant women should avoid all contact with teratogens, particularly during the first three months of pregnancy, as this can result in damage to the developing child. For example, alcohol is a teratogen and drinking during pregnancy can lead to a child born with fetal alcohol syndrome. Many drugs can also have an adverse effect on developing fetuses, the most infamous example being thalidomide. This drug was originally used to control morning sickness, but was withdrawn from the market after it was discovered to cause limb and other developmental deformities. It is now on the market again for various ailments, with very prominent warnings about its fetotoxicity. There are few examples of transplacental carcinogens, substances which can cause fetuses exposed during pregnancy to eventually develop cancer. The best-known example is DES, diethylstilbestrol, a compound formerly used to prevent miscarriages before its trans-generational carcinogenic activity was known. MSDS Relevance: Always minimize the use and release of teratogens (or believed teratogens) in the workplace. Women who are of child-bearing age should pay particular attention to teratogenic materials because they could be pregnant without knowing it and expose their fetus. Teratogens typically cause their most severe damage during the first 3 months of pregnancy, a period during which many pregnancies are not yet known. Many teratogens cause effects at very low exposure levels. See also: Clastogen, Mutagen, Carcinogen