There is theoretical concern, and animal evidence, that environmental hormones and
chemicals may affect aspects of prenatal or postnatal sexual development in humans. Large amounts of incompletely metabolized estrogens and
progestagens from pharmaceutical products are excreted into the sewage systems of large cities, and are sometimes detectable in the environment.
Sex steroids are sometimes used in cattle farming but have been banned in chicken meat production for 40 years. Although agricultural laws regulate use to minimize accidental human consumption, the rules are largely self-enforced in the United States. Significant exposure of a child to hormones or other substances that activate estrogen or androgen
receptors could produce some or all of the changes of puberty.
Harder to detect as an influence on puberty are the more diffusely distributed environmental chemicals like PCBs (
polychlorinated biphenyl), which can bind and trigger estrogen receptors.
More obvious degrees of partial puberty from direct exposure of young children to small but significant amounts of pharmaceutical sex steroids from exposure at home may be detected during medical evaluation for
precocious puberty, but mild effects and the other potential exposures outlined above would not.