There are a number of terms that have been applied to the chemicals in the environment that are believed to affect the endocrine system. These include endocrine disrupters, hormonally active agents, environmental estrogens and endocrine modulating substances.

An endocrine disruptor has been defined as "as an exogenous agent that interferes with the synthesis, secretion, transport, binding, action or elimination of natural hormones in the body that is responsible for the maintenance of homeostasis, reproduction, development and/or behaviour" (USEPA 1997). It is also described as an "exogenous substance that causes adverse health effects in an intact organism or its progeny, subsequent to changes in endocrine function (EC 1997).

"Endocrine disruption" refers to the fact that there is negative interference or permanent adverse consequences beyond the range of everyday fluctuations of hormone levels.

There is considerable controversy surrounding the use of these terms. For instance, some scientists disagree with the use of the term "disrupter". They argue that these chemicals may either over or under modulate the activity of a particular hormone and not necessary "disrupt" the endocrine system. Furthermore, the human health consequences of these chemicals are still not clearly understood. The academic community, government and the media has predominantly used the term "endocrine disrupting chemicals". For more information on terminology, see our fact sheet on What Is An Endocrine Disrupter?

The group of hormones believed to be most susceptible to the action of endocrine active chemicals is steroids. Steroid hormones are produced in the gonads; namely the testes of males and the ovaries of females. The male steroids are termed androgens, the main one being testosterone. Androgens that are produced early in the development of an embryo will direct its development as a male. At puberty, high concentrations of androgens are responsible for the development of human male secondary sexual characteristics such as male patterns of hair growth and deepening voice. The female steroids are estrogens and progestins. The main estrogenic chemical is estradiol while the predominant progestin is progesterone. During puberty, as the ovaries mature, the levels of estrogens and progestins increase. This leads to the initiation of the menstrual cycle, breast development and increases in uterine tissue, broadening of the pelvis and increases in the levels of subcutaneous fat. For more information on hormones, visit our Endocrine Primer