Babies go through a mini-puberty, and hormones keep shifting for the rest of your life

Key takeaways

• In the first months after birth, babies go through a “mini-puberty”: boys’ testosterone peaks between 1 and 3 months, and girls’ FSH, a pituitary hormone, can stay high until age 3 or 4.
• Across 30 studies done from 1977 to 2013, the age when girls’ breasts began to develop fell by almost 3 months per decade.
• Signs of puberty before age 8 in girls or 9 in boys meet NICHD’s definition of early puberty, which affects no more than about 1 in 100 people in the U.S.
• Men’s testosterone may start a slow slide around ages 30 to 40, while menopause usually arrives between 45 and 55; any bleeding after a full year without periods should be checked.
• In a two-year trial of 144 older adults, DHEA didn’t improve strength, body makeup or quality of life, and distributing growth hormone outside authorized medical uses is a federal crime.

Within minutes of birth, a baby boy’s pituitary gland, at the base of the brain, sends out a hormone called LH at about 10 times its earlier level. His testosterone spikes for 12 to 24 hours¹.

Then things quiet down, but only briefly. Within days, the signals return, and the hormones that will drive puberty years later rise again. Doctors call this second wave “mini-puberty”¹.

Many parents never hear of it. Yet it’s an early sign of something true for life: your hormones never stand still. They surge in infancy, wake up at puberty, transform in pregnancy, shift in midlife and drift lower with age.

Most of those changes are normal design, not damage. A few signal disease and deserve a checkup. And some get sold as problems a pill or shot can reverse, with little proof and, in one case, a federal law in the way.

This article walks through each stage. Menopause and pregnancy each get their own upcoming articles in our library.

Babies go through a “mini-puberty” in their first months

In a 2020 review in Frontiers in Endocrinology, researchers C. Bizzarri and M. Cappa laid out the timeline¹. The second hormone wave starts once the mother’s placental estrogens clear from the baby’s blood, which takes a few days¹.

In boys, testosterone peaks between 1 and 3 months of age¹. The penis grows about 1 millimeter a month from birth to 3 months, and the testicles grow too¹. By around 7 months, testosterone is low again¹.

In girls, the pituitary hormone FSH climbs from about the second week of life, hits its high point sometime in the first 3 months and can stay elevated until age 3 or 4¹. Estrogen stays up, with ups and downs, for at least 6 months, and breast tissue that a parent can feel often persists¹.

Why would the body do this? In boys, mini-puberty may help set up how the testicles work for life, the review says. In girls, its role is still unclear¹. Studies have linked these early hormones with later behavior, but those links are correlations, not proof¹.

Mini-puberty also gives doctors a window. A blood sample at 4 to 8 weeks of age can confirm congenital hypogonadism, a condition in which the body makes too little sex hormone from birth, faster and more accurately than tests done later¹. One clue is an undescended testicle. It shows up in about 25% of babies with this condition, compared with 1% to 3% of full-term babies overall¹.

Puberty is starting earlier than it did in the 1970s

Puberty is the same hormone chain switching back on. The hypothalamus, at the base of the brain, sends GnRH to the pituitary gland. The pituitary releases LH and FSH, which tell the ovaries or testes to make estrogen or testosterone².

NICHD, the National Institutes of Health’s child-health institute, says puberty typically starts between 8 and 13 in girls and between 9 and 14 in boys². Our article on puberty’s normal range explains how wide that span is.

What has changed is the timing for girls. In 2020, a team led by researchers at the University of Copenhagen reviewed studies from around the world in JAMA Pediatrics. Across 30 studies done between 1977 and 2013, the age when breast buds first appeared fell by 0.24 years per decade, almost 3 months³.

By our math, if that trend held steady across the 36 years the studies spanned, breast development began about 10 months earlier by the end than at the start. In U.S. studies, the typical starting age ranged from 8.8 to 10.3 years³.

The authors said doctors need current data to redefine “early” puberty, since the traditional cutoff may be outdated in some places³. Most of the studies came from Europe and North America³. The main analysis measured timing, not causes.

NICHD lists obesity as a risk factor for early puberty², and our article on endocrine disruptors covers the chemical questions.

Early or late puberty: when a child should be checked

NICHD defines precocious, or early, puberty as signs starting before age 8 in girls or before age 9 in boys². It’s rare, touching no more than about 1 in 100 people in the U.S., and girls far more often than boys².

In most cases, doctors find no cause². Sometimes the trigger is a brain or hormone-gland problem, severe hypothyroidism, or a child’s contact with a medicine or skin cream containing estrogen or male-type hormones such as testosterone².

Early puberty can stop growth early and leave a child shorter as an adult. Some children also struggle socially or emotionally, though many don’t². Not every child needs treatment, especially if puberty is only a little early. When treatment is needed, drugs that mimic GnRH can suppress LH and FSH and pause puberty².

Late puberty matters too. Cincinnati Children’s Hospital describes delayed puberty as no breast development by 13 in girls, or little to no genital growth by 14 in boys⁴.

Often it simply runs in families. A parent who developed late raises the odds²⁴. Long-term illness, and hormone problems such as Turner syndrome in girls, can also be causes².

A pediatrician checks puberty against the five Tanner stages and may order blood tests and a bone-age X-ray².

Pregnancy rewrites the hormone script

Pregnancy changes hormones fast. The best-known marker is hCG, the hormone pregnancy tests detect. It can show up in blood and urine as soon as 10 days after conception. It climbs fast through the first trimester, then dips slightly⁵.

The normal ranges are startlingly wide. At 7 weeks, MedlinePlus lists hCG anywhere from 4,059 to 153,767 mIU/mL⁵. By our math, the top of that range is about 38 times the bottom. So a single number says little on its own.

A lower-than-expected level can go along with miscarriage or ectopic pregnancy⁵. That’s a hard thing to wait on, and your clinician is the right person to interpret it.

Pregnancy changes other tests, too. The protein that carries thyroid hormone in the blood normally rises in pregnancy, which changes how thyroid results read⁶. Our upcoming pregnancy articles cover nutrition, sleep, nausea and the rest.

Midlife: a bumpy transition for women, a gentle slope for men

For women, the years before the last period are the transition called perimenopause. MedlinePlus says it can begin several years before the final period⁸. Periods may come more often at first, then get skipped, and some cycles shrink to about three weeks⁷⁸. This irregular stretch can run one to three years⁷.

Menopause usually arrives between about 45 and 55 and is confirmed after 12 months without a period⁷⁸. The ovaries make less estrogen and progesterone⁷. Until a full year has passed, pregnancy is still possible, so MedlinePlus says birth control should continue⁸.

Blood tests can help, but estradiol, FSH and LH may need repeating while periods are still coming⁷. Our upcoming menopause articles cover symptoms and treatment, and our menopause sleep guide covers nights.

Men have no single turning point. Testosterone may start falling slowly around ages 30 to 40 as a normal part of aging⁹. A 2025 review contrasts that gradual slope with the abrupt hormone drop women go through in midlife¹⁰. That’s why “male menopause” is a misleading name.

Low testosterone can cause low sex drive, erection problems, poor sleep, lost muscle and low mood⁹. But some men have no symptoms, and diabetes and high blood pressure can cause similar problems⁹. Obesity, low thyroid, some medicines and pituitary problems can also lower testosterone⁹. Our upcoming testosterone article covers testing and treatment.

Later life: some hormones fade, and cortisol’s daily rhythm flattens

Several hormones fall with age. The 2025 review in Exploration of Endocrine and Metabolic Diseases says growth hormone, its partner IGF-1, and melatonin all decline¹⁰. In people over 60, growth hormone output drops, and IGF-1 follows, a change researchers call the “somatopause”¹⁰.

DHEA, an adrenal hormone the body uses to make testosterone and estrogen, peaks around puberty and declines as you get older, according to MedlinePlus¹¹.

Cortisol behaves differently. Average daily levels tend to rise with age, and the normal daily swing, high in the morning and low at night, flattens¹⁰. Evening and nighttime cortisol run higher¹⁰.

Thyroid changes are less clear. The same review says the role of TSH, the pituitary’s thyroid signal, in aging is still being studied¹⁰. Our article on thyroid function explains how to read an older adult’s results.

If you trust the body’s wisdom, this is a useful frame. A lower level in later life is often the body’s normal setting for that age, not a deficiency to be topped up. The question to ask is whether a change is causing a problem a test can confirm.

“Anti-aging” hormones: unproven, and sometimes illegal to sell

DHEA. DHEA supplements are sold over the counter and sometimes promoted as anti-aging therapy¹¹. MedlinePlus says there’s no reliable evidence for those claims and that the supplements may cause serious side effects¹¹.

A careful test came from the Mayo Clinic. In a two-year, double-blind trial published in the New England Journal of Medicine in 2006, researchers gave DHEA, low-dose testosterone or a placebo to adults over 60 with low hormone levels¹²¹³. Among 57 women, 27 took DHEA and 30 a placebo. Among 87 men, 29 took DHEA, 27 testosterone and 31 a placebo¹².

DHEA didn’t improve body composition, muscle strength, fitness, insulin sensitivity or quality of life¹². Both hormones produced small bone-density gains at single sites, smaller than standard osteoporosis drugs deliver¹²¹³. The researchers concluded that neither works as an anti-aging supplement¹³.

Growth hormone. Here the law is unusually blunt. Under 21 U.S.C. 333(e), it’s a federal crime to knowingly distribute human growth hormone, or hold it in order to distribute it, for anything other than treating a disease or recognized medical condition that federal health officials have authorized, on a doctor’s order¹⁴¹⁵. Clinics selling it to slow aging have to fit inside that narrow lane. It carries up to 5 years in prison, or up to 10 if someone under 18 is involved¹⁴.

The FDA enforces it. In 2019, the agency moved to bar a man from importing drugs after his 2018 conviction over imported growth hormone sold for bodybuilding and other unapproved uses¹⁵. The FDA noted possible long-term risks of growth hormone, including higher cancer risk, nerve pain, and higher cholesterol and blood sugar¹⁵.

Testosterone. Prescribed testosterone treats a diagnosed deficiency. Our article on longevity clinics covers what a major heart-safety trial found.

Hormones by life stage, and when to get help

Stage	What’s changing	What’s normal	What to check	Source
Birth to about 6 months	Mini-puberty	Boys’ testosterone peaks at 1 to 3 months; girls’ breast tissue often lingers	Doctors can test at 4 to 8 weeks if hypogonadism is suspected	1
Ages 8 to 14	Puberty	Girls start between 8 and 13, boys between 9 and 14	Signs before 8 in girls or 9 in boys; no breasts by 13 or no genital growth by 14	24
Pregnancy	hCG, thyroid carrier protein	hCG rises fast, with very wide normal ranges	One result means little alone; thyroid tests read differently	56
Women, about 40s to 50s	Perimenopause, then menopause	Irregular periods for 1 to 3 years; menopause around 45 to 55	Spotting between periods; any bleeding after 12 months without one	78
Men, from 30s on	Slow testosterone decline	A gradual slope, not a sudden stop	Lasting symptoms such as no interest in sex or erection problems	9
After 60	Growth hormone, DHEA, melatonin fall; cortisol rhythm flattens	Lower levels can be normal for age	Ask before taking any hormone product	1011

Get a check when one of these applies:

• A child shows puberty signs before 8 in girls or 9 in boys. That meets NICHD’s definition of early puberty, which a pediatrician can evaluate².
• A girl has no breast development by 13, or a boy has little to no genital growth by 14. Cincinnati Children’s lists these as signs of delayed puberty⁴.
• You have spotting between periods, or any bleeding after 12 months without a period. MedlinePlus says to contact a provider, because bleeding after menopause may be an early sign of problems such as cancer⁷.
• Symptoms of low testosterone are bothering you. A provider will likely order a blood test and check other causes, such as thyroid problems, medicines and depression⁹.
• You’re thinking about DHEA or another hormone product for aging. Talk with a clinician first; MedlinePlus warns of possible serious side effects¹¹.

Our upcoming article on reproductive symptoms lists the emergencies, such as signs of ectopic pregnancy, that can’t wait.

How strong is the evidence?

Claim	Rating	Why
Healthy babies go through mini-puberty	Strong evidence	Consistent hormone measurements summarized in a 2020 review1
Girls’ breast development starts earlier than in the 1970s	Strong evidence	2020 meta-analysis of 30 studies; mostly Europe and North America3
Mini-puberty shapes later behavior	Promising but early	Correlations only1
Men’s testosterone declines gradually from around 30 to 40	Strong evidence	Described as normal aging by MedlinePlus and a 2025 review910
DHEA supplements slow aging	Evidence says no, or unsafe	No real benefit in a two-year placebo-controlled trial12

Questions readers ask

The bottom line

Hormones change at every stage of life, from a baby’s mini-puberty to the slow fades of old age. Most of those shifts are the body doing what it was built to do. Puberty now starts earlier for many girls, and a few changes, such as very early or late puberty or bleeding after menopause, deserve a prompt look.

What the evidence doesn’t support is the promise that youth can be bottled. DHEA failed a careful two-year trial, and distributing growth hormone outside authorized medical uses can bring prison time. The better path is to learn what’s normal for your stage and check the changes that aren’t.

Related reading

• Puberty’s normal range is far wider than parents expect
• Hot flashes aren’t the only thing stealing sleep in menopause
• How to sort longevity clinics that mix proven care with pricey experiments
• Babies borrow their mothers’ antibodies, and older adults’ infections may bring no fever
• Hormones run on feedback loops and clocks, which is why one test can mislead

Sources

1. Bizzarri C, Cappa M. “Ontogeny of Hypothalamus-Pituitary Gonadal Axis and Minipuberty: An Ongoing Debate?” Frontiers in Endocrinology, 2020;11:187. frontiersin.org
2. Eunice Kennedy Shriver National Institute of Child Health and Human Development. “Puberty and Precocious Puberty.” NIH, accessed October 2026. nichd.nih.gov
3. Eckert-Lind C, Busch AS, Petersen JH, et al. “Worldwide Secular Trends in Age at Pubertal Onset Assessed by Breast Development Among Girls: A Systematic Review and Meta-analysis.” JAMA Pediatrics, 2020;174(4):e195881. pubmed.ncbi.nlm.nih.gov
4. Cincinnati Children’s Hospital Medical Center. “Delayed Puberty.” Health Library, updated October 2025. cincinnatichildrens.org
5. MedlinePlus Medical Encyclopedia, National Library of Medicine. “HCG blood test – quantitative.” Reviewed October 15, 2024. medlineplus.gov
6. MedlinePlus Medical Encyclopedia, National Library of Medicine. “TBG blood test.” Reviewed January 25, 2026. medlineplus.gov
7. MedlinePlus Medical Encyclopedia, National Library of Medicine. “Menopause.” Reviewed July 3, 2025. medlineplus.gov
8. MedlinePlus Medical Encyclopedia, National Library of Medicine. “Aging changes in the female reproductive system.” Reviewed October 15, 2024. medlineplus.gov
9. MedlinePlus Medical Encyclopedia, National Library of Medicine. “Could you have low testosterone?” Reviewed April 24, 2025. medlineplus.gov
10. Coggins C, Patel S, Nigam S, Rai V. “Hormonal changes during aging and their effects on quality of life.” Exploration of Endocrine and Metabolic Diseases, 2025;2:101447. explorationpub.com
11. MedlinePlus, National Library of Medicine. “DHEA Sulfate Test.” Updated June 5, 2024. medlineplus.gov
12. Nair KS, Rizza RA, O’Brien P, et al. “DHEA in elderly women and DHEA or testosterone in elderly men.” New England Journal of Medicine, 2006;355:1647–1659 (abstract via PubMed). pubmed.ncbi.nlm.nih.gov
13. MDedge. “DHEA, testosterone show no antiaging benefits.” December 1, 2006. mdedge.com
14. Legal Information Institute, Cornell Law School. “21 U.S. Code § 333 – Penalties,” subsection (e), “Prohibited distribution of human growth hormone.” Accessed October 2026. law.cornell.edu
15. U.S. Food and Drug Administration. “Proposal to Debar; Notice of Opportunity for Hearing” (Jagen D. Lewicki), Docket No. FDA-2019-N-3131, September 25, 2019. fda.gov