Microplastics have been found inside human testicles, semen, placentas, and ovarian tissue, and a growing body of evidence links them to measurable changes in reproductive function. Whether they directly cause infertility in humans isn’t fully settled, but the picture emerging from both human tissue studies and animal research is concerning: microplastics appear to reduce sperm motility, damage egg quality, disrupt reproductive hormones, and carry endocrine-disrupting chemicals deep into reproductive organs.
Microplastics Are Already in Reproductive Organs
Researchers have now confirmed that microplastics aren’t just passing through the body. They’re accumulating in the tissues most critical to reproduction. A study analyzing human testicular tissue found an average of 11.6 particles per gram, with polystyrene making up nearly 68% of the plastic detected. Semen samples from the same research contained microplastics too, though at lower concentrations, averaging 0.23 particles per milliliter. The dominant plastic types in semen were polyethylene (common in plastic bags and bottles) and polyvinyl chloride (PVC).
The placenta tells a similar story. In one longitudinal analysis, 60% of placentas collected in 2006 contained microplastic particles. By 2013, that rose to 90%. By 2021, every single placenta tested was positive. Multiple independent studies have now found microplastics in 100% of placentas examined, with particles ranging from 2 to 100 micrometers. The most common polymers include polyethylene, polypropylene, polystyrene, and PVC. These particles have also been detected in amniotic fluid, meconium, breast milk, and newborn stool, confirming that fetuses are exposed before birth.
Effects on Sperm Quality
In men whose semen contained PET microplastics (the polymer used in water bottles and food packaging), progressive sperm motility averaged 20.6%, compared to 34.9% in men without PET exposure. That’s a roughly 40% relative reduction in the sperm’s ability to swim forward effectively. The same group also showed a higher percentage of completely immotile sperm: 66.7% versus 51.1%. Importantly, microplastic presence in semen did not correlate with differences in total sperm count or concentration, suggesting that the damage may be more about sperm function than sperm production.
Animal studies help explain why. In mice, microplastic exposure triggers inflammation in testicular tissue and breaks down the blood-testis barrier, a protective structure that normally shields developing sperm cells from toxins in the bloodstream. Smaller nanoplastics (particles under 1 micrometer) cross this barrier more easily by being absorbed directly into cells. Once inside, they interfere with the chemical pathways that support sperm cell development, particularly thyroid hormone signaling and energy metabolism in the cells that nourish maturing sperm.
Effects on Eggs and Ovarian Function
The damage to female fertility may be equally significant. In animal models, microplastic exposure reduces the number of developing follicles (the structures in the ovaries that contain eggs) and lowers levels of Anti-Müllerian hormone, a key marker of ovarian reserve. Exposed mice produced more poor-quality eggs, with problems including disrupted spindle assembly during cell division, misaligned chromosomes, and abnormal distribution of mitochondria, the structures that supply eggs with the energy they need to be fertilized and develop into embryos.
Hormone production shifts as well. Cell studies show that micro- and nanoplastic exposure alters the balance of reproductive hormones, increasing some forms of progesterone while decreasing estriol (a form of estrogen) by up to 37.5%. These hormonal disruptions affect the entire chain of events required for ovulation, fertilization, and early pregnancy. Researchers have linked microplastic exposure to disrupted steroidogenesis (the process by which ovarian cells produce sex hormones) and even to conditions like polycystic ovary syndrome in experimental models.
The Chemical Cargo Problem
Microplastics don’t just cause harm on their own. They act as tiny delivery vehicles for a cocktail of endocrine-disrupting chemicals. Plastics absorb and concentrate substances like bisphenols (including BPA), phthalates, flame retardants, and heavy metals, many of which are added during manufacturing. Because these chemicals aren’t permanently bonded to the plastic, they leach out once inside the body, particularly in warm, fluid-rich environments like reproductive tissue.
This matters because even at low concentrations, endocrine disruptors can mimic or block hormones that regulate fertility. In animal studies, microplastics contaminated with phthalates accumulated in testicular tissue and reduced both sperm count and vitality. The combination of the plastic particle itself plus the chemicals it carries creates a dual threat: physical disruption of cells and tissues, layered on top of chemical interference with hormonal signaling. The list of associated disorders includes infertility, early puberty, hormone-driven tumors, and metabolic problems.
Risks During Pregnancy and for Future Generations
Perhaps the most alarming findings involve exposure during pregnancy. Microplastics cross the placenta and reach the developing fetus, where they’ve been detected in fetal brain tissue. Animal studies show that prenatal exposure can alter fetal body weight and organ development, with some of these changes persisting into adulthood. Offspring of exposed mice showed changes in metabolic function, with some sex-specific differences in how those effects played out.
There are also signs that the reproductive damage could span generations. When pregnant animals were exposed to endocrine-disrupting chemicals carried by plastics (BPA and phthalates specifically), researchers observed ovarian disease, testicular abnormalities, obesity, and pubertal disruptions not just in the first generation of offspring, but in the second and third generations as well, with the third generation often showing the most pronounced effects. This suggests that microplastic-associated chemicals may trigger epigenetic changes, alterations to how genes are expressed that get passed down without changing the DNA itself.
Infants affected by intrauterine growth restriction linked to these exposures face elevated long-term risks for cardiovascular disease, type 2 diabetes, and metabolic syndrome, particularly if they experience rapid “catch-up” growth in early life.
What We Know and What We Don’t
The core question of whether microplastics cause human infertility sits in a difficult evidentiary space. The biological mechanisms are well-documented: microplastics damage the protective barriers around reproductive cells, disrupt hormonal signaling, impair egg and sperm quality, generate oxidative stress, and deliver endocrine disruptors to sensitive tissues. Human tissue studies confirm that the particles are present in exactly the places where this damage would matter. And the correlations between microplastic presence and reduced sperm motility in human semen are striking.
What’s missing is the kind of long-term, large-scale human data that would establish a definitive causal link at real-world exposure levels. Most dose-response studies have been conducted in animals, often at concentrations higher than what humans typically encounter. No established safety threshold exists for microplastic exposure as it relates to fertility. And because everyone is now exposed to some degree, finding an unexposed control group is essentially impossible.
The trajectory of the evidence, however, points in one direction. Microplastic concentrations in human tissue appear to be increasing over time, the biological pathways for reproductive harm are clearly identified, and the chemicals they carry are already classified as reproductive toxicants. The gap between “strongly implicated” and “proven cause” is narrowing with each new study.