They also initiate puberty and later play a role in the regulation of sexual behavior. The major sex hormones can be classified as estrogens or androgens. Both classes of hormones are present in males and females alike, but in vastly different amounts. Estrogens are also present in both sexes, but in larger amounts for women. Estrogens are the sex hormones produced primarily by a female's ovaries that stimulate the growth of a girl's sex organs, as well as her breasts and pubic hair, known as secondary sex characteristics.
Estrogens also regulate the functioning of the menstrual cycle.
In the majority of women, ovarian hormones appear not to play a significant role in their sex drive. Estrogens are important in maintaining the condition of the vaginal lining and its elasticity, and in producing vaginal lubrication. They also help preserve the texture and function of a woman's breasts. In men, estrogens have no known function. An unusually high level, however, may reduce sexual appetite, cause erectile difficulties, produce some breast enlargement, and result in the loss of body hair in some men.