When Does Puberty Start and When Does It End?

Boys often begin adolescence at age 9, and girls as young as eight years old can kick off puberty without sounding any clinical alarm bells.

Puberty starts earlier than you think, even in healthy children. Boys often begin adolescence at age nine, and girls as young as eight years old can kick off puberty without sounding any clinical alarm bells. “There’s data suggesting the age of onset for girls may be getting younger, and some have actually advocated lowering that boundary to seven or even six,” Dr. Phillip Lee, director of pediatric endocrinology at The University of Texas Medical Branch told Fatherly.

“Personally, I think that’s too young.”

When puberty starts and ends are confusing subjects for parents, but Lee breaks it down in simple, clinical terms. In boys, healthy puberty begins with testicular enlargement, which should occur no earlier than age 9 and no later than 14. In girls, healthy puberty can start any time after age 8; breast development should kick in by age 13 and the first period should occur before 15. Andronarche, which is when the adrenal glands produce androgen precursors that cause initial hair growth in the pubic and underarm regions, usually starts about one year before that.

When healthy puberty ends is harder to say. “Usually the physical part of puberty takes three to four years to complete, although the growth spurt can go on a bit longer,” Lee says. “The landmark in girls is the first menstrual cycle. In boys, there’s not a clearly defined endpoint.”

Within these age ranges, all is considered normal. Outside of those age ranges, doctors worry. “In boys, late puberty is usually a physiological event, a constitutional delay, with a longer and less dramatic growth spurt. Puberty tends to end later or take a bit longer,” Lee says. “Late puberty is not common in girls, and is more likely to be an abnormal physiological event.”

Puberty may start late due to a pituitary disorder, hyperthyroidism, or syndromes that affect the ovaries or testicles. Early puberty can be caused by hypothyroidism, or brain and spinal cord injuries. One strange factor that may causes early puberty is exposure to testosterone. “It’s not that uncommon,” Lee says. “Guys can buy topical androgens in health food stores, for bodybuilding. If they pick up a young kid, it can transfer right through their skin and trigger the body to start its own puberty. You want to be careful about exposing children to topical steroids.”

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Regardless of the cause, doctors usually address both early and late puberty with more or less the same initial battery of tests. “In the first visit, we’ll run one set of blood tests for puberty and thyroid hormones, and then an x-ray to assess skeletal age,” Lee says.

“That would occur whether puberty is early or late.”