agent that causes the production of physical defects in the developing embryo

A teratogen is a material that can cause birth defects. Teratogens include some chemicals, medications, and infectious diseases. The name goes back to Ancient Greek "theras", which can be translated as "monster".

This symbol shows that a substance is damaging to human health. This includes substances that cause birth defects.

About 75% of all birth defects are caused by teratogens.[1][2]p. 23-3

Types of teratogens


Alcohol and illegal drugs


Alcohol is the most common cause of congenital disorders that can be prevented.[3] Alcohol is poisonous to a fetus and can cause brain damage.[4] Drinking alcohol while pregnant can cause the fetus to get fetal alcohol syndrome.[3]

Illegal drugs, like heroin and cocaine, are also poisonous to the fetus and can cause many different congenital problems. For example, cocaine use during pregnancy can cause microcephaly (a smaller head size than usual) and problems with the way the fetus's urinary system and genitals grow.[1]


Baby born to a mother who took thalidomide while pregnant

Some medications can also hurt the fetus if its mother takes them while she is pregnant. For example:[1][2]p. 23-6

Before the 1960s, many countries did not have rules about testing medications for their effects on fetuses.[5] This changed partly because of thalidomide. This medication was given to pregnant women for nausea in the 1950s and 1960s. Between 1956 and 1962, more than 10,000 children in 46 different countries were born with birth defects, like arms and legs that had not grown.[6] Thalidomide had not been tested well enough before it started being prescribed.[6] Now, many countries require more testing before a medication can be said to be safe during pregnancy.[5]


This baby was born with cataracts (cloudy white lenses in the eyes) caused by rubella

If a woman gets an infection while she is pregnant, sometimes the infection can affect her fetus. The placenta protects the fetus from many different viruses, bacteria, and other pathogens that cause infections. However, some pathogens can get through the placenta and infect the fetus. This is called vertical transmission. Some of these infections can cause birth defects.

Examples of infections that can cause birth defects include:



Some chemicals can cause birth defects, if a pregnant woman is exposed to enough of them. For example:[11]

  • Lead: If a woman ever had lead poisoning, she can pass lead on to her fetus, even if she is not exposed to lead while she is pregnant. This happens because most lead is stored in a person's bones and can come out into the bloodstream many years later. Lead can cause miscarriage and stillbirth as well as birth defects.
  • Mercury: High levels of mercury can cause brain damage in fetuses.

Other things


High levels of ionizing radiation can cause birth defects.[2]p. 23-8

Things that are not teratogens


Examples of things that do not cause birth defects include:[11]


  1. 1.0 1.1 1.2 "Things to Avoid During Pregnancy: Teratogens". AboutKidsHealth. The Hospital for Sick Children. Retrieved February 17, 2016.[permanent dead link]
  2. 2.0 2.1 2.2 Chung, Wendy (2004). "Teratogens and Their Effects". The New Public Health: An Introduction for the 21st Century. New York: Columbia University Press. ISBN 978-0127033501.
  3. 3.0 3.1 "Facts about FASDs". cdc.gov. United States Centers for Disease Control and Prevention (CDC). April 16, 2015. Retrieved February 14, 2016.
  4. "Fetal Alcohol Syndrome". ncbi.nlm.nih.gov. United States National Library of Medicine. Retrieved December 28, 2015.
  5. 5.0 5.1 Tantibanchachai, Chanapa (January 22, 2014). "Teratogens". The Embryo Project Encyclopedia. Arizona State University. ISSN 1940-5030. Retrieved February 14, 2016.
  6. 6.0 6.1 Bren L (February 28, 2001). "Frances Oldham Kelsey: FDA Medical Reviewer Leaves Her Mark on History". FDA Consumer. U.S. Food and Drug Administration. Retrieved February 14, 2016.
  7. "STDs during Pregnancy – CDC Fact Sheet". CDC.gov. United States Centers for Disease Control and Prevention. February 3, 2016. Retrieved February 9, 2016.
  8. Torgerson, Paul R; Mastroiacovo, Pierpaolo (2013-07-01). "The global burden of congenital toxoplasmosis: a systematic review" (PDF). Bulletin of the World Health Organization. 91 (7): 501–508. doi:10.2471/BLT.12.111732. ISSN 0042-9686. PMC 3699792. PMID 23825877.
  9. Boussault, Pierre; Boralevi, Franck; Labbe, Laurence; Sarlangue, Jean; Taïeb, Alain; Leaute-Labreze, Christine (July 2007). "Chronic Varicella-Zoster Skin Infection Complicating the Congenital Varicella Syndrome". Pediatric Dermatology. 24 (4): 429–432. doi:10.1111/j.1525-1470.2007.00471.x. ISSN 0736-8046. PMID 17845179. S2CID 22389596.
  10. "Congenital Rubella Syndrome - Vaccine Preventable Diseases Surveillance Manual | CDC". www.cdc.gov. 2022-04-06. Retrieved 2022-04-09.
  11. 11.0 11.1 Gilbert-Barness E 2010 (20 March 2010). "Teratogenic Causes of Malformations". Annals of Clinical & Laboratory Science. 40 (2). Association of Clinical Scientists, Inc.: 99–114. PMID 20421621. Retrieved February 2, 2016.{{cite journal}}: CS1 maint: numeric names: authors list (link)