Teratogens are agents or factors that can disturb the normal development of an embryo or fetus, resulting in structural abnormalities, functional deficits, growth retardation, or even fetal death. In environmental toxicology, teratogens are significant because they originate from natural, biological, and anthropogenic environmental exposures. Understanding their sources, effects, and mechanisms is essential for preventing developmental disorders and protecting maternal and fetal health. Teratogens can act during critical periods of prenatal development, especially during organogenesis, when organs are forming and cells are rapidly dividing and differentiating. Various sources of teratogens exist in the environment, and these can be broadly classified into chemical, physical, biological, and maternal or lifestyle-related sources. Chemical teratogens are among the most common and include industrial chemicals, pesticides, heavy metals, drugs, and environmental pollutants. Industrial chemicals such as polychlorinated biphenyls (PCBs), dioxins, and organic solvents can enter the body through air, water, or food contamination. Heavy metals like lead, mercury, arsenic, and cadmium are known teratogens. Mercury exposure, especially in the form of methylmercury through contaminated fish consumption, can cause neurological defects and developmental delays in the fetus. Pesticides used in agriculture can contaminate food and water sources and may interfere with normal fetal growth and development. Pharmaceutical drugs are another major chemical source of teratogens. Certain medications taken during pregnancy can interfere with normal embryonic development. For example, some anti-epileptic drugs, retinoids used for acne treatment, and certain chemotherapeutic agents can cause congenital malformations. Alcohol and tobacco are