Thelarche is the first stage of human breast development, usually occurring at the beginning of puberty in girls. Thelarche is usually noticed as a firm, tender lump directly under the center of the nipple (papilla and areola). Thelarche is also referred to as a "breast bud", or more formally as Tanner stage 2 breast development (Tanner stage 1 being the entirely undeveloped prepubertal state). Thelarche may occur on one side first, or both sides simultaneously.
Thelarche is usually the first physical change of puberty in girls, and is a result of rising levels of estradiol.
Although breast development can occur as a part of normal male puberty, it is termed gynecomastia, and the term "thelarche" is not used with reference to male development.
