One System. One Story.
How the chemicals affecting fertility, development and reproductive health across a lifetime are connected to what women experience in perimenopause and menopause.
When you look at the work of the researchers and doctors featured on this site separately, they each appear to be studying different problems. Sperm count decline. Chemical exposure in children. Pesticides and fertility. Atrazine in water. Perimenopause. Menopause.
But they are not studying different problems. They are all studying the same system from different angles, at different points in a human life. The endocrine system. The network of hormones, glands and receptors that governs virtually every process in the human body from the moment of conception until the end of life.
This page connects those dots. Because understanding the full picture changes how you think about all of it.
The System Everything Runs On
The endocrine system is the body's chemical messaging network. Hormones are its messengers. They travel through the bloodstream and attach to receptors in cells throughout the body, telling those cells what to do. Grow. Stop growing. Release energy. Store fat. Produce sperm. Prepare an egg. Build bone. Regulate mood. Manage sleep.
Because estrogen, testosterone, thyroid hormones and dozens of other chemical messengers govern so many processes simultaneously, disrupting this system has consequences that ripple across every organ and every stage of life.
Endocrine disrupting chemicals work by mimicking these messengers, blocking them or altering how the body produces and responds to them. They do not need to be present in large quantities to cause harm. Some of the most significant effects occur at extremely low concentrations, precisely because the body's own hormones operate at vanishingly small levels.
The same chemicals affecting sperm counts in men are affecting egg quality in women, fetal development in the womb, neurological development in children, and the hormonal transition of perimenopause and menopause. This is one story told across a lifetime.
Before Birth: Trasande and Grandjean
Dr Leonardo Trasande, a paediatrician at New York University, has spent his career documenting what happens when the endocrine system is disrupted during the most critical window of all: fetal development. His phrase, womb to tomb, captures the central insight of his work. The chemical exposures a mother experiences during pregnancy do not stay with the mother. They cross the placenta. They shape the developing child.
Researchers now find microplastics in human placentas. They find PFAS in cord blood. They find phthalates altering the hormonal environment of the developing fetus. The consequences include changes to reproductive organ development, altered hormone levels at birth and effects on neurological development that persist into adulthood.
Dr Philippe Grandjean, a physician and epidemiologist at Harvard, has documented how PFAS chemicals impair immune function so fundamentally that children exposed to higher levels produce significantly fewer antibodies after vaccination. His work shows that the thyroid hormone system, which governs brain development in fetal life, is particularly vulnerable to chemical disruption. The damage, once done during development, cannot be undone.
The window before birth is when chemical exposure matters most. But it sets up the hormonal environment that every subsequent stage of life builds on.
The Reproductive Years: Swan and Hayes
Dr Shanna Swan is an epidemiologist whose research has tracked one of the most significant public health trends of our time: the 62% decline in sperm counts between 1973 and 2018, with the rate of decline accelerating after 2000. Her book Count Down makes the case that this is not a male problem. It is a signal from the endocrine system that something in the modern chemical environment is disrupting reproductive biology across the board.
Her research connects phthalates, BPA, PFAS and other endocrine disrupting chemicals to measurable changes in testosterone levels, sperm quality, egg quality and fertility outcomes. The same chemicals. The same system. Now expressing itself through the reproductive health of adults.
Dr Tyrone Hayes, a biologist at UC Berkeley, demonstrated that atrazine, one of the most widely used herbicides in the world, disrupts sex hormone signalling so profoundly that male frogs exposed to it developed female reproductive organs. His work, and the extraordinary corporate pressure he faced in attempting to publish it, revealed how deeply the agricultural chemical industry was embedded in the regulatory process supposed to protect public health.
Together, Swan and Hayes document what happens when the endocrine system is chronically disrupted during the years it is most actively engaged in reproduction. Lower fertility. Altered hormonal profiles. A reproductive system working against a chemical environment it was never designed to navigate.
The Menopause Connection: Haver
Dr Mary Claire Haver is an OBGYN who returned to study after two decades in clinical practice because she realised her training had left her profoundly unprepared to help the women going through perimenopause and menopause who sat in front of her every day. Her work has reached millions of women and is credited with helping to shift the conversation around menopause in medicine and in public life.
What connects her work to the others on this page is this: the endocrine system that Swan documents declining in reproductive years, and that Trasande and Grandjean show being disrupted from before birth, is the same system that Haver describes breaking down during perimenopause and menopause. Estrogen does not just govern reproduction. It protects bones, regulates the cardiovascular system, supports the brain, maintains muscle mass and governs dozens of other processes. When it declines, everything it was protecting becomes vulnerable.
And research published in 2024 and 2025 has now confirmed what this site has been arguing: that chemical exposure specifically affects how women experience the menopause transition. A 2024 study in Environment International found that phthalate exposure was associated with measurable changes in sex steroid hormones across the perimenopausal period. Harvard research confirmed that everyday chemicals in personal care products and food packaging alter hormone levels during this transition.
A woman who has spent decades accumulating chemical exposure during her reproductive years arrives at perimenopause with an endocrine system already under pressure. The transition was always going to be significant. The question is how much additional burden the chemical environment is placing on a system already working hard to adapt.
The choices that protect hormonal health during the reproductive years are the same choices that support the transition through perimenopause and beyond. This is not a coincidence. It is because they are all expressions of the same underlying system.
What This Means in Practice
Understanding that this is one system with one story changes how you think about the practical choices available to you.
It is not about fertility or about menopause or about child development. It is about protecting the system that underpins all of these simultaneously. The same swap from conventional to organic produce, the same choice of glass over plastic, the same avoidance of synthetic fragrance, serves every stage of life.
The research on fetal development shows that the earliest windows matter most. But the body is constantly responding to its chemical environment. Reducing exposure at any point produces benefits. Women in perimenopause who reduce their phthalate and PFAS exposure are supporting the same hormonal system that is already under pressure from estrogen decline.
The researchers on this site are not alarmists. They are scientists who have followed the evidence wherever it led, often at significant professional and personal cost. Their message is not that the situation is hopeless. It is that the situation is understood, and that understanding it makes practical action possible.
The choices available to individuals matter. But so does the regulatory environment that determines which chemicals are permitted in food, water, packaging and consumer products. The researchers on this site have all argued, with evidence, for stronger regulation. Supporting that argument, alongside making personal choices, is part of the same response.
Meet the Experts Behind This Research
Each of the researchers and doctors referenced on this page has a dedicated Expert Talk page on this site, with video content, research summaries and direct links to their published work.
FERTILITY
Dr Shanna Swan
Sperm count decline, phthalates and the future of human reproduction.
PESTICIDES
Dr Tyrone Hayes
Atrazine, sex hormone disruption and the cost of speaking truth to power.
CHILD HEALTH
Dr Leonardo Trasande
Chemical exposure from womb to tomb and the economic cost of inaction.
PFAS AND IMMUNITY
Dr Philippe Grandjean
PFAS chemicals, immune function and neurological development in children.
WOMEN'S HEALTH
Dr Mary Claire Haver
Perimenopause, menopause, HRT and why the medical system has failed women.
THE BIGGER PICTURE
Jeremy Grantham
Why one of the world's most respected investors believes chemical exposure is the defining health crisis of our time.
These researchers did not set out to tell the same story. They followed the evidence in their own fields over decades of work. But the story they have collectively uncovered is the same one. The endocrine system is under pressure from a chemical environment it was not designed to handle. And that pressure is being felt at every stage of human life.
Understanding this does not make it more frightening. It makes it clearer. And clarity is where action begins.
Explore the Full Picture Interactively
The map below shows how the problem, the causes, the evidence and the solutions all connect. Hover over any node to see what it links to. Click to go deeper.
Sources: Swan SH, Count Down (2021) | Hayes TB et al, PNAS (2010) | Trasande L, Sicker Fatter Poorer (2019) | Grandjean P et al, JAMA (2012) | Haver MC, Diary of a CEO interview (2023) | Babadi RS et al, Environment International (2024) | Harvard T.H. Chan School of Public Health (2025) | Campen MJ et al, Toxicological Sciences (2024)