A number of different hormones make your breasts grow over your lifetime. The period of greatest breast growth is in puberty. As an adult, you may wonder if hormones can cause further breast growth. Later, in maturity, you might ponder over where your breasts went, and if you can get them back again. The hormones that affect breast growth are powerful, but the way that they interact is complex. So, our ability to harness the power of hormones for breast growth is limited.
The primary sex hormone in a woman's body is estrogen. Estrogen is produced by the ovaries throughout a woman's life. Estrogen levels are lowest in childhood and after menopause. At puberty, estrogen levels spike, promoting the maturation of the reproductive organs and the growth of the breast tissues and pubic and underarm hair. Progesterone and testosterone are also produced by the ovaries, but these are not as responsible for breast growth as estrogen.
Estrogen production does not begin spontaneously. At puberty, the brain produces gonadotropin-releasing hormones which trigger the pituitary to produce the hormones called gonadotropins. The primary gonadotropins that act on the ovaries are luteinizing hormone, or LH, and follicle-stimulating hormone, FSH. LH and FSH cause the ovaries to boost estrogen production. This increase in pituitary and gonadal hormones only occurs in puberty, which is why the dramatic breast growth of puberty cannot be duplicated later.
Genetic body fat distribution plays a major role in breast growth. So, the size the female breast attains during puberty is highly variable between individuals. A woman who is predisposed to have little fat on the chest wall will ultimately have small breasts. This does not affect the functional breast tissues or ability to lactate.
Hormones cause breast size to change slightly throughout a woman's life. During pregnancy estrogen levels rise, and a woman will notice an increase in breast size. Part of this is due to swelling of the mammary tissues, and part is due to body fat gain. When estrogen begins to decline after age 35, the functional breast tissues involute, or shrink. A decrease in estrogen also causes a woman's body fat to become redistributed in a more childlike pattern--away from the breasts and buttocks, and toward the belly.
Breasts may seem to grow in response to estrogen supplementation. Estrogen replacement therapy can cause breast swelling and tenderness similar to pregnancy or premenstrual phases. Herbal supplements like saw palmetto or wild yam, which containing phytoestrogens, can have a similar effect. In both cases though, breast size will revert to normal when the estrogen or phytostrogens are discontinued.