Microplastics Have Been Found in Human Reproductive Fluids. What Does the Research Say?

What the Study Actually Found

The research, led by Dr. Emilio Gómez-Sánchez, director of the assisted reproduction laboratory at Next Fertility Murcia in Spain, in collaboration with the University of Murcia, was presented on July 1, 2025, at the 41st Annual Meeting of the European Society of Human Reproduction and Embryology, or ESHRE, in Paris. The team analyzed follicular fluid, the liquid that surrounds and nourishes a developing egg inside an ovarian follicle, from 25 to 29 women, and seminal fluid from 18 to 22 men, all of whom were undergoing fertility evaluation.

Microplastics were detected in 69 percent of the follicular fluid samples and in 55 percent of the seminal fluid samples. Imaging identified nine distinct polymer types across both fluids, including polytetrafluoroethylene, polystyrene, polyethylene terephthalate, polyamide, polypropylene, and polyurethane. In the follicular fluid samples, polytetrafluoroethylene, more commonly known by the brand name Teflon, was the single most frequently detected polymer, found in 31 percent of samples, followed by polypropylene at 28 percent and polyethylene terephthalate, the plastic used in most beverage bottles, at 17 percent.

The research has not yet completed peer review at the time of presentation, a status the study authors and outside experts were careful to flag publicly. It was presented as a conference abstract, the standard first step for emerging findings in reproductive medicine, with the full paper expected to appear in the journal Human Reproduction. This finding did not arrive in isolation. A separate 2024 study out of China detected microplastics in every human semen sample tested, while an earlier Italian study found them in 60 percent of healthy men, and additional 2025 research reported microplastics in all 23 human testicle samples examined in that cohort.

Why Researchers Were Not Entirely Surprised, But Were Struck by the Scale

"Previous studies had already suggested this possibility, so the presence of microplastics in the human reproductive system is not entirely unexpected," Gómez-Sánchez said in a statement provided to the press at the time of the ESHRE presentation. "What did surprise us, however, is how widespread it is. This is not an isolated finding. It appears to be quite common." The research team also noted an unexpected asymmetry: follicular fluid showed a higher rate of microplastic detection than semen, even though the sample sizes were broadly comparable. Gómez-Sánchez offered a possible physiological explanation rather than a confirmed one, since the study group was small. When an ovary is stimulated as part of assisted reproduction, blood flow to the ovary increases substantially, which may deliver a greater volume of circulating microplastic particles to the follicular environment during that window.

Professor Carlos Calhaz-Jorge, immediate past chair of ESHRE, offered the field's official framing of what the finding does and does not establish. "Environmental factors influencing reproduction are certainly a reality, although not easy to measure objectively," he said. "The authors of this study found microplastics in over two-thirds of follicular fluids and more than 50 percent of semen fluids from the studied patients. Although the significance of these findings is not yet clear, they should be considered an additional argument in favor of avoiding the generalized use of plastics in our daily lives."

The Biological Mechanisms Under Investigation

Detecting microplastics inside reproductive fluid is a different question from proving that those particles are causing reproductive harm in humans, and researchers are careful to separate the two. What does exist is a growing body of animal and cell-based research describing plausible biological pathways through which microplastics could affect fertility, even though much of this evidence has not yet been confirmed at the doses and durations people actually experience.

The most consistently documented mechanism is oxidative stress. Microplastic particles appear to interfere with electron transfer inside cells, triggering the overproduction of reactive oxygen species that damage cell membranes, proteins, and DNA. In sperm cells specifically, this process has been linked in laboratory studies to reduced motility, lower vitality, and increased sperm DNA fragmentation, a marker clinicians already use to assess male fertility. A 2025 in vitro study exposing human semen samples directly to polystyrene microplastics found that sperm vitality and motility declined in a time-dependent manner following exposure, alongside downregulation of several genes required for sperm to successfully fuse with an egg.

In animal studies, the effects on the ovary follow a parallel pattern. Mice exposed to polystyrene microplastics in drinking water showed ovaries that weighed less and produced fewer mature follicles, the structures that contain developing eggs, alongside clear biochemical signs of oxidative stress in ovarian tissue. Separate research in rats found that polystyrene microplastics induced ovarian granulosa cell death through oxidative stress, contributing to ovarian fibrosis and reduced ovulation. A second proposed mechanism involves microplastics acting as carriers for endocrine-disrupting chemicals such as bisphenol A and phthalates, compounds already established in the scientific literature as capable of mimicking or blocking natural hormone activity, with documented associations in human studies to altered estradiol, progesterone, and testosterone levels.

• Oxidative stress is the most consistently documented mechanism, observed in both human sperm cell studies and animal ovarian tissue studies
• Microplastics can act as carriers for endocrine-disrupting chemicals already linked to reproductive hormone disruption
• Mitochondrial dysfunction has been identified in rat studies as a key pathway linking microplastic exposure to impaired sperm energy production and testicular damage
• Researchers caution that most mechanistic evidence currently comes from animal models and cell cultures, not confirmed human reproductive outcomes

What Remains Genuinely Unknown

The scientific caution surrounding this research is not a formality. A formal review published through the National Center for Biotechnology Information, examining the threat of micro- and nanoplastics to male fertility specifically, concluded that while laboratory and animal data point to multiple plausible mechanisms of testicular toxicity, including disruption of the blood-testis barrier and structural damage to testicular tissue, significant limitations remain in extrapolating those results directly to human physiology. Differences in exposure routes, doses, and species-specific biological responses all complicate the translation from animal findings to confirmed human risk.

A clinical trial currently registered to formally investigate this question, described in public trial documentation as non-interventional, is explicit that its hypothesis, while biologically plausible and supported by emerging experimental evidence, has not yet been confirmed in human reproductive outcomes at real-world exposure levels. Researchers studying micro- and nanoplastics broadly have also noted that humans are exposed to these particles through multiple simultaneous routes, ingestion of food and water, inhalation of airborne particles, and absorption through skin contact, which makes isolating the reproductive effect of plastic exposure specifically, separate from other co-occurring environmental and lifestyle factors, a genuine methodological challenge.