Thelarche is the first stage of seconary (postnatal) 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.