Which is a teratogen?

• A. Acrylonitrile
• B. Ethanol
• C. Benzene
• D. Acetaminophen (Tylenol)

Answer: (A)

Teratogens are substances that cause birth defects or developmental problems when a fetus is exposed during pregnancy. Ethanol is a well-established teratogen because it readily crosses the placenta and can disrupt multiple developmental processes, especially in early pregnancy. This interference can lead to fetal alcohol spectrum disorders, which include facial abnormalities, growth problems, and neurodevelopmental issues. The outcome depends on how much alcohol is consumed and when during development—the greater the exposure, the higher the risk, with early exposure typically causing more serious effects. The other substances listed have toxic effects, but they are not classically described as teratogens in standard medical toxicology: acrylonitrile and benzene are primarily noted for general toxicity and carcinogenic risk, and acetaminophen is commonly used during pregnancy at recommended doses without the same clear pattern of birth defects associated with ethanol.