Perhaps the most important hormones influencing gender expression are androgens, a class of steroid hormones. Androgens, including testoterone, are produced in every person regardless of sex. High levels of androgens are responsible for the development of internal and external genetalia for males during prenatal development. An absense of high levels of these hormones leads to the development of internal and external genetalia for females.

In addition to influencing prenatal development, androgens have activating influences on the brain and body. Hormones fluctuate depending on factors such as emotions, experiences, and perceived danger. These factors are subjective, and therefore vary depending on one's gender role, associated stereotypes, and life experiences.