Microplastics, Polyester Clothing & Human Health

What Are Microplastics?

Microplastics are microscopic plastic particles—most often fibers or fragments—small enough to move through air, water, indoor environments, and even the human body. Rather than being defined by a single size threshold, microplastics are identified by their behavior: they are plastics that have broken down into particles capable of being inhaled, ingested, and transported biologically.

The most relevant particles for human exposure are typically in the 1–500 micrometer range—far too small to see with the naked eye. These include:

• Microfibers shed from synthetic textiles such as polyester, nylon, and acrylic. Research confirms that the most abundant microfibers released during washing are typically 360–660 µm in length and 12–16 µm in diameter.
• Fragments generated as larger plastics degrade.
• Nanoplastics, particles smaller than 1000 nanometers (1 µm), which are small enough to cross biological membranes, including the gut and blood-brain barriers.

Studies of indoor air and household dust show that textile-derived microfibers are the dominant type of microplastic humans encounter indoors. In fact, synthetic fragments and fibers can account for a significant portion of inhalable particles, with indoor air concentrations ranging between 1.0 and 60.0 fibers per cubic meter—significantly higher than outdoor concentrations.

Polyester: A Leading Source of Microplastic Exposure

Polyester is a synthetic plastic fiber. When worn, washed, or dried, it sheds microfibers that accumulate in air and dust. Modern research identifies polyester clothing as one of the largest direct sources of human microplastic exposure.

Polyester sheds microplastics during normal wear

Wear, friction, and movement of polyester garments release microfibers into indoor air, where humans spend most of their time. These lightweight fibers can remain suspended and are easily inhaled. In controlled studies of indoor environments using breathing thermal manikins, polyester was found to be the predominant synthetic polymer, accounting for 81% of all synthetic particles identified in the air.

Washing polyester releases huge microfiber loads

Laundry studies show a single synthetic garment can shed hundreds of thousands of fibers per wash. A landmark experiment documented that a single wash of synthetic clothes (approx. 2–2.5 kg load) releases between 124 and 308 mg of microfibers per kg of fabric. This translates to a massive release of approximately 640,000 to 1,500,000 individual microfibers per wash cycle.

The structure of the fabric dictates the release volume:

• Knitted vs. Woven: Loose, knitted structures (common in t-shirts) often release significantly more fibers than tightly twisted, woven fabrics.
• The Blend Problem: Washing mixed fabrics (polyester/cotton blends) can actually release higher amounts of fibers than 100% polyester, with the mechanical friction causing heavy shedding of both plastic and cellulosic fibers.

Dryers emit airborne polyester fibers

Household tumble dryers vent large quantities of airborne microfibers, many of them polyester. Research indicates that a single dryer can release between 433,128 and 561,810 microfibers into the air during just 15 minutes of use. It is estimated that the average household releases over 90 million microfibers annually from a single dryer, directly contaminating the ambient air.

Recycled polyester can shed even more

Recent work suggests recycled-PET fabrics often release more fibers than virgin polyester under identical washing conditions, due to differences in yarn structure and previous degradation. In comparative tests, recycled polyester released significantly more microfibers (1193 fibers vs. 908 fibers for virgin polyester), likely due to the reduced mechanical strength of the polymer chains caused by the recycling process.

Polyester vs. natural fibers

Natural fibers (cotton, linen, hemp, wool) also shed, but they are not plastics. They are primarily cellulose or protein-based and biodegrade differently from persistent synthetic polymers like PET. Polyester fibers are persistent microplastics that accumulate indoors, in the environment, and in the body.

How Microplastics Enter the Human Body

1. Inhalation (the largest route from clothing)

Indoor air often contains higher concentrations of microplastics than outdoor air—concentrations can be up to 60 times higher indoors. Measurements using a "Breathing Thermal Manikin" designed to simulate human physiology found that an average male doing light activity inhales up to 272 microplastics every 24 hours. Because these particles are often small (median size 36 µm) and fibrous, they can bypass the body's upper airway defenses and deposit deep in the lungs.

2. Ingestion

Microplastics are found in bottled water, tap water, sea salt and other foods. A major vector is household dust fallout, which settles on meals and surfaces at a rate of 1,586 to 11,130 fibers per day per square meter. This settled dust poses a specific risk to young children due to crawling and hand-to-mouth behaviors. Studies of human stool samples detected microplastics in all participants, confirming regular ingestion and incomplete elimination.

3. Internal transport

Nanoplastics and small microplastics can cross epithelial barriers and enter the bloodstream, enabling transport to organs. Once inside, they act as "Trojan Horses," carrying toxic additives like bisphenols, phthalates, and heavy metals into tissues. Experimental work has shown model nanoplastics crossing the blood–brain barrier in controlled settings.

Microplastics in Brain & Where Else Microplastics Have Been Detected in Humans

• Brain — Recent analysis of human autopsy specimens revealed that the brain accumulates significantly higher concentrations of microplastics (primarily polyethylene) than the liver or kidneys. The study found a rising trend in exposure, with brain samples from 2024 containing approximately 50% more plastic than those from 2016. Furthermore, brain samples from patients with dementia exhibited significantly higher plastic loads (median 26,076 µg/g) compared to those without the condition.
• Blood — Plastic particles were detected in venous blood samples of patients undergoing surgery, proving they circulate through the vascular system. In healthy volunteers, plastic particles were found in 77% of donors, with a mean concentration of 1.6 µg/ml. PET (used in clothing) and polyethylene were the most widely encountered.
• Lungs — Polyester and acrylic fibers have been found in deep lung tissue from surgical patients. In a study of 13 lung tissue samples, microplastics were identified in 11 of them, with polypropylene and PET fibers being the most abundant.
• Arterial Plaque — In a major study of 304 patients with carotid artery disease, 58.4% of patients had detectable polyethylene in their excised arterial plaque, and 12.1% had measurable polyvinyl chloride. Electron microscopy revealed jagged-edged foreign particles embedded inside immune cells (macrophages) within the plaque.
• Heart tissue — Microplastics have been detected in completely enclosed human organs, including the pericardium, myocardium (heart muscle), and epicardial adipose tissue. The largest particle found in heart tissue was 469 µm in diameter.
• Placenta — Pigmented microplastic fragments found on both maternal and fetal sides of the human placenta, suggesting these particles can cross the most protective biological barriers.

Collectively, these findings support the idea that microplastics are now biological contaminants as well as environmental ones.

What Microplastics May Be Doing Inside Us

The health science is developing rapidly, and recent studies have established alarming links between microplastic accumulation and severe health outcomes.

Cardiovascular death and stroke risk

The presence of microplastics in arterial plaque is linked to severe outcomes. Patients with microplastics in their plaque had a 4.53 times higher risk of suffering a myocardial infarction (heart attack), stroke, or death within 34 months compared to those without plastics in their plaque.

Chronic inflammation and oxidative stress

Microplastics provoke inflammatory responses. In arterial plaque, the presence of plastics was directly correlated with higher levels of inflammatory markers like Interleukin-18 and TNF-α. Electron microscopy reveals immune cells actively trying to engulf these jagged foreign particles, which may make plaques more unstable and prone to rupture.

Endocrine disruption (The "Trojan Horse" Effect)

Plastics act as vectors, or "Trojan Horses," carrying endocrine-disrupting chemicals (EDCs) like bisphenols, phthalates, and flame retardants into the body. These chemicals leach into tissues and disrupt the body's delicate control systems:

• Thyroid: Exposure is linked to reduced thyroid hormones (T3/T4), which are essential for metabolism and brain development. Flame retardants found in plastics (PBDEs) specifically suppress thyroid hormone synthesis.
• Reproduction: In males, microplastics can penetrate the blood-testis barrier, leading to reduced testosterone, sperm deformities ("headless" sperm), and oxidative stress. In females, they accumulate in ovaries, reducing follicle growth and potentially contributing to conditions like PCOS.

Neuroinflammatory risks

Evidence that nanoplastics can reach brain-related tissues has raised concern about neuroinflammation. Nanoplastics can accumulate in the hypothalamus, potentially disrupting the hormonal command center that regulates stress, growth, and reproduction.

What Scientists Still Don’t Know

• At what exact dose exposure becomes critically harmful for the general population.
• How toxicity differs between specific polymer types beyond polyethylene and PVC.
• The lifetime effects of exposure beginning in infancy, particularly regarding neurodevelopment and the blood-brain barrier.

Reducing Exposure to Microplastics (and Why We Use Only Natural Fibers)

Current evidence points to synthetic clothing as one of the most direct and controllable sources of exposure.

At ShirtCastle™, we respond by choosing:

• 100% natural fibers only
• No polyester
• No synthetic blends

By building your wardrobe around plastic-free fabrics, you reduce the microplastics you shed, breathe, ingest, and carry into your home.

References

1. Nihart AJ et al. (2025). Bioaccumulation of microplastics in decedent human brains. Nature Medicine. Link
2. Leslie HA et al. (2022). Discovery and quantification of plastic particle pollution in human blood. Environment International. Link
3. Jenner LC et al. (2022). Detection of microplastics in human lung tissue using μFTIR spectroscopy. Science of the Total Environment. Link
4. Vianello G et al. (2019). Simulating human exposure to indoor airborne microplastics using a Breathing Thermal Manikin. Scientific Reports. Link
5. Dris R et al. (2017). A first overview of textile fibers, including microplastics, in indoor and outdoor environments. Environmental Pollution. Link
6. De Falco F et al. (2019). The contribution of washing processes of synthetic clothes to microplastic pollution. Scientific Reports. Link
7. Tao Y et al. (2022). Microfibers Released into the Air from a Household Tumble Dryer. Environmental Science & Technology Letters. Link
8. Akyildiz SH et al. (2024). Release of microplastic fibers from synthetic textiles during household washing. Environmental Pollution. Link
9. Ragusa A et al. (2020). Plasticenta: First evidence of microplastics in human placenta. Environment International. Link
10. Yang Y et al. (2023). Detection of Various Microplastics in Patients Undergoing Cardiac Surgery. Environmental Science & Technology. Link
11. Schwabl P et al. (2019). Detection of Various Microplastics in Human Stool: A Prospective Case Series. Annals of Internal Medicine. Link
12. Marfella R et al. (2024). Microplastics and Nanoplastics in Atheromas and Cardiovascular Events. New England Journal of Medicine. Link
13. Ullah S et al. (2023). A review of the endocrine disrupting effects of micro and nano plastic and their associated chemicals in mammals. Frontiers in Endocrinology. Link
14. Shan S et al. (2022). Polystyrene nanoplastics penetrate across the blood-brain barrier and induce activation of microglia in the brain of mice. Chemosphere. Link

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