Global secular trends in timing of puberty

During the last century, several studies from the United States and Europe have demonstrated a secular trend towards earlier pubertal onset, particularly in girls. The initial clinical sign of pubertal onset is breast development in girls and testicular enlargement larger than 3 mL in boys. This review briefly describes the physiology of normal puberty and sexual maturation, historic and recent secular changes in age at pubertal onset in girls and boys as well as changes in the incidence of precocious puberty. Furthermore, the possible mechanisms explaining the recent advancement in the onset of puberty are discussed.