(like pesticides, bisphenol-A*, and phthalates)
Endocrine disruptors (or hormone disruptors) are chemicals that are capable of disrupting the normal functioning of our endocrine and immune system. This disruption causes our hormones to become unbalanced, and our immune system to malfunction. Additionally, these chemicals are capable of affecting the human reproductive system, causing infertility, miscarriages, and abnormal development of the human fetus in a mother's uterus.
Hormone disruptors act by masquerading as endogenous (made in our own body) hormones. If the body sees the toxin as a 'hormone', it will allow that toxin to do the things in the body that the hormone does. So, for example, if the chemical is masquerading as estrogen (estrogenic), and the affected human happens to be a 7 year-old girl, premature puberty (breast development, menarche) may ensue.
Hormone disruptors can also disrupt the body's ability to make (and break down) it's own hormone. This would leave a shortage of hormone in some instances, and an excess of hormone in others. They can also block the body's ability to make and maintain hormone receptors.
In the end, these chemicals are like a monkey wrench in the very balanced hormone milieu of our body.
Hormones are essential to human survival, and species propagation. Estrogen, progesterone, testosterone, insulin, glucagon, and thyroxine (thyroid hormone) are all very well-known hormones. Our hormones are synthesized in various glands in our body. Then, when the conditions are "right" (and what is right for one hormone depends on the environment in our body), the gland releases it's hormone. The hormone circulates in the blood, and attaches to it's receptor. The receptor is located on the tissue or organ where the action of the hormone will take place. Once the hormone is attached to the receptor, a cascade of events leads to the desired action.
For instance, in mammals, the sex hormones attach to receptors, and this attachment causes a fetus to either differentiate into a girl baby, or a boy baby. Testosterone is responsible for the development of a penis/scrotum, and other obvious *male* characteristics. Without testosterone (or without testosterone receptors, or in the presence of a *hormone disruptor* which blocks the action of testosterone) the male fetus cannot develop into a phenotypical male human. So the newborn will not have a penis (or the penis will not be fully developed or normally functioning). Additionally, there are many scientists who believe that the worldwide decline in sperm production in the last 50 years is attributed to the exposure of male fetuses to excess estrogenic chemicals in utero. This is what is known as demasulinization.
There is also speculation that testicular cancer, prostate cancer, and breast cancer are all increasing (despite medical advancement, and the entire "Thinking Pink" money-making brainwashing scam every October) because our exposure to estrogenic hormone disruptors are increasing.
Thyroid hormone is important to regulate our metabolism, and is important during growth and development of the brain. Without it, we die. Hormone disruptors may cause the thyroid hormone levels to decline, leading to hypothyroidism. Hypothyroidism causes many undesirable effects, such as hair loss, cold intolerance, and weight gain. In fetuses, thyroid hormone defiency is reported to cause delayed mental development and low IQ scores.
*bisphenol-A which is commonly found in plastics (some to make baby bottles) is a known hormone disruptor.