Which of the following describes a teratogen?

A teratogen is specifically defined as an agent capable of causing congenital defects in a developing fetus. This includes a range of substances such as certain medications, chemicals, and even infections that can interfere with normal embryonic development. The impact of teratogens can vary depending on the timing of exposure during pregnancy, the dose, and the genetic susceptibility of the fetus.

Understanding this definition is crucial in fields like environmental health, as it underscores the importance of identifying and controlling exposures that could harm fetal development. The other options refer to different concepts: an agent promoting growth relates to positive influences on development rather than harmful effects. A substance that causes disease can refer to many pathogens or toxins but doesn't specifically entail prenatal developmental impacts. Lastly, a type of infectious pathogen refers to organisms that cause disease, which does not inherently imply teratogenic effects unless specified.