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Microplastics and nanoplastics may injure the body when particles or the chemicals attached to them interact with cells. The best-supported chain is oxidative stress and immune activation, followed by inflammation, impaired cellular barriers and mitochondria, altered endocrine or metabolic signals, DNA damage, and sometimes cell death. Human studies have detected particles in blood and organs and found biomarker associations, but they have not yet proved that ordinary environmental exposure causes a specific chronic disease in an individual.
What counts as a microplastic, and how does it enter the body?
Microplastics are generally defined as plastic particles up to 5 millimetres across. Nanoplastics are smaller particles, often able to interact with cells in different ways because their size gives them a high surface area relative to their mass.
People are exposed mainly by swallowing particles in food or water and by inhaling airborne particles. Skin exposure is considered possible, although the extent to which particles cross intact human skin is less certain. Once inhaled or swallowed, particles can contact airway or intestinal linings, pass into body fluids, or be taken up by immune and other cells.
Reviews have reported microplastic or nanoplastic particles in human blood, urine, feces, placenta, lung, liver, kidney, brain and cardiovascular tissues. Reported burdens differ substantially because laboratories use different collection, detection and contamination-control methods; a detection result is not, by itself, a measure of disease risk.
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The proposed damage pathway, step by step
- Contact with a cell. A particle can touch a cell membrane, lodge at a tissue barrier, or carry additives and environmental chemicals on its surface. Weathering can change the particle’s surface and make it chemically different from a newly manufactured laboratory sphere.
- Cell uptake or persistent irritation. Immune cells and epithelial cells can engulf particles. Larger particles may remain at a surface and stimulate nearby cells even when they are not internalized.
- Oxidative stress. Particle–cell interactions can increase reactive oxygen species. If antioxidant defenses cannot compensate, oxidative stress can damage proteins, lipids and genetic material.
- Innate-immune activation. The stressed cell can release signaling molecules that recruit or activate immune cells. Repeated signaling may sustain local inflammation rather than resolve it quickly.
- Barrier, metabolic and endocrine effects. Studies propose disruption of intestinal or airway barriers, mitochondrial function, metabolism and hormone signaling. These effects are not expected to be identical for every polymer or dose.
- Cell injury or death. Severe stress can trigger apoptosis, a regulated form of cell death, or necrosis, which can release additional inflammatory signals.
Particle size, polymer chemistry, dose, exposure duration, surface weathering and co-contaminants all influence this sequence. A clean particle used in a short cell experiment is therefore not interchangeable with a weathered environmental mixture encountered over months or years.
What the March 2025 cell study found
A primary study by Brandon Bishop, William S. Webber, Wei Zhang, Suzhao Li and colleagues, published in Frontiers in Immunology on 31 March 2025, tested commercial and environmental microplastic and nanoplastic samples in several human cell systems.
| Human model | Reported response | What it indicates |
|---|---|---|
| Monocytes and other immune-cell systems | Release of interleukin-1 beta (IL-1β) and interleukin-6 (IL-6) | Activation of inflammatory signaling |
| Whole-blood and peripheral-blood cultures | Inflammatory cytokine responses | Blood components can respond directly to particles in culture |
| Intestinal epithelial cells | Release of interleukin-8 (IL-8) | Inflammatory signaling at a gut-barrier model |
| Exposed cultures overall | Apoptosis and necrosis after exposure | Evidence of cellular injury at the tested concentrations |
PET-rich particles were especially active in the experiments. Environmental samples often produced stronger effects than pure commercial PET. The authors considered mixed polymers and chemicals attached to weathered surfaces as possible explanations, rather than assuming that PET alone accounts for the response.
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What studies in people show
A 2025 systematic review of in-vivo human evidence identified five cardiovascular studies involving 454 people, three respiratory studies involving 171 people and one ocular study involving 49 people. Across these small and heterogeneous studies, higher particle burdens were correlated with inflammatory markers, adverse cardiac events and some airway or ocular findings.
Another human-focused systematic review found recurring associations with C-reactive protein (CRP), IL-6, tumour necrosis factor alpha (TNF-α), thyroid hormones, cortisol, 8-hydroxy-2′-deoxyguanosine (8-OHdG) and malondialdehyde. Inflammatory and endocrine biomarkers showed more consistent associations than neurocognitive outcomes or broad chronic-disease measures.
| Evidence type | What it can show | Main limitation |
|---|---|---|
| Cell cultures | Direct particle effects, cytokine release and cell injury under controlled conditions | Doses and exposure times may not match ordinary human exposure; no whole-body clearance or disease process |
| Human observational studies | Particle burdens, biomarkers and clinical events occurring together | Small samples, variable detection methods and confounding cannot prove that particles caused the outcome |
| Human disease causation | A specific exposure causing a named disease in an individual | Not established for ordinary environmental microplastic exposure |
These findings make the biological mechanism plausible, but they do not prove that microplastics cause cancer, heart disease, infertility, dementia or another particular illness at environmental exposure levels. A correlation can reflect particle effects, another exposure that travels with them, pre-existing disease, or measurement differences.
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Why particle type and dose change the answer
Polymer and surface chemistry
PET-rich particles were unusually inflammatory in the 2025 experiments, but that result should not be generalized to every PET item or every plastic polymer. Additives, dyes, manufacturing residues and pollutants can adsorb to a particle. Sunlight, abrasion and oxidation can roughen a surface and alter how cells recognize it.
Size and route
Nanoplastics may cross or interact with biological barriers differently from larger microplastics. An inhaled particle first encounters airway tissue; a swallowed particle encounters the gut and may be removed in feces, absorbed, or transported onward. The same nominal mass can therefore produce different biological exposure depending on particle number, size distribution and route.
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Duration and dose
Short, high-dose experiments are useful for identifying possible pathways but cannot predict the effect of low-dose exposure repeated over decades. Human dose estimates remain difficult because sampling, digestion, spectroscopy and contamination controls are not standardized.
What is established—and what is still unknown
- Established: people encounter microplastics through food, water and air, and studies have detected particles in multiple human tissues and fluids.
- Strongly supported as mechanisms: oxidative stress, inflammatory signaling and changes to cellular barriers and organelle function.
- Supported but less settled: endocrine and metabolic disruption, DNA damage and particle-driven cell death in particular tissues.
- Not established: a dose threshold for disease, a reliable conversion from measured particle burden to personal risk, or causal proof for a named chronic disease.
Detection methods and burden estimates need better harmonization, and studies must distinguish clean reference particles from weathered, chemically complex environmental mixtures. Long-term human studies that measure exposure before disease develops are especially important.
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Can people prevent or treat microplastic injury?
No consumer product is proven to treat an injury caused by microplastics. Certified household water filtration is being studied as one way to reduce particulate exposure, but performance varies by device and particle size. A filter should not be described as removing all microplastics or preventing disease unless independent testing demonstrates those specific claims.
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For now, the medically responsible position is exposure reduction where practical, while recognizing that scientists cannot yet translate an individual’s measured or estimated particle burden into a precise health forecast. Anyone with symptoms should seek ordinary medical evaluation rather than attributing them to microplastics without evidence.
The bottom line from the new evidence
Microplastics can plausibly damage cells through a connected sequence of particle contact, oxidative stress, immune activation, barrier and mitochondrial disruption, altered hormonal or metabolic signaling, and apoptosis or necrosis. The 2025 Frontiers in Immunology study strengthens the case that both laboratory and environmental particles can provoke inflammatory responses in human cell models, with PET-rich and weathered mixtures showing notable activity. Human studies, however, remain too small and inconsistent to prove that everyday environmental exposure causes a particular chronic disease.
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