Thelarche

Thelarche ( /θɨˈlɑrkiː/) is the onset of secondary (postnatal) breast development, usually occurring at the beginning of puberty in girls. Its etymology is from Greek θηλή, “nipple” and ἀρχή, “beginning, onset”. Thelarche is usually noticed as a firm, tender lump directly under the centre 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.