It has been shown that a very broad range of chemical agents can produce, under the proper conditions, some serious type of developmental deviation. Substances already found to be embryopathic in animals range from highly toxic substances, such as anti-tumour agents, to commonplace consumer items such as aspirin, and completely inert materials. There are 33 known and proven teratogens. Known agents include: chemical factors (methylmercury, aminopterin, thalidomide, iodine deficiency, steroid hormones with androgenic activity, carbon monoxide); infective micro-organisms (rubella virus, herpes virus, cytomegalovirus, toxoplasma, syphilis); physical factors (ionizing radiation, trauma and perhaps high temperatures).
With the increasing number of women employed in industry, environmental pollution due to industrial wastes, the use of insecticides, herbicides and defoliants constitute a definite potential hazard for the human embryo.