Abstract

Premature thelarche is a rare medical condition that is characterized by isolated breast development (thelarche being the onset of breast development) at a very early age with no other signs of sexual maturation. It generally occurs within the first 1 to 4 years of life, with a peak incidence of 2 years of age, and tends to resolve within 1 to 2 years without treatment. The condition never advances beyond Tanner stage III breast development.

Premature thelarche is distinct from neonatal breast hyperplasia (see also witch's milk), which is common in the first few months of life and is due to acute exposure to high levels of sex hormones like estrogen during pregnancy. Premature thelarche is also distinct from precocious puberty, which generally occurs later in childhood and also includes development of other pubertal characteristics.

Treatment with fennel ("Foeniculum vulgare") has been associated with premature thelarche in several case reports. Estradiol levels were found to be elevated by 15–20 times for the ages of the afflicted girls (5 months to 5 years). Also, fennel is known to contain anethole, an estrogenic compound.