The breathing zone
1.7 to 16.2
particles per cubic metre of indoor air at breathing height
Vianello's team put a breathing mannequin in three Danish apartments and analysed what it drew in. Every sample carried microplastic, between 1.7 and 16.2 particles per cubic metre. Polyester was 81 percent of the synthetic fibres.
Breathed
Strong evidence
What changes it. Most of a day is spent indoors, so the count at breathing height indoors describes exposure better than an outdoor reading does.
Sources:
Vianello 2019
The nose and the swallow
About 60 percent
of the mass deposited in the airway reaches the oesophagus within a day
Lazaridis and colleagues applied published air concentrations to a dosimetry model of the human respiratory tract. Inhaled particles settled mostly in the nose and throat. After one day the model put about 60 percent of the deposited mass into the oesophagus, 28 percent still in the airway and 0.4 percent into the bloodstream.
Breathed, Swallowed
Modelled evidence
What changes it. Most of what is breathed in is swallowed rather than kept, which is why the two routes are hard to separate in any single measurement.
Sources:
Lazaridis 2026
·
Islam 2023
The mouth
Up to 637
microplastics released into saliva per gram of chewing gum
Lowe's team chewed five natural and five synthetic gums and counted what came off into saliva. Each gram released up to 637 microplastics, 94 percent of them in the first eight minutes. The median particle measured 45.4 micrometres.
Swallowed
Emerging evidence
What changes it. Plant-based gums released about as many as synthetic ones in this test, so the label is not a guide here.
Sources:
Lowe 2025
The hands
1.85, then 4.2
particles counted on a child's hands, arriving and then leaving
Amiri and colleagues swabbed the hands and sampled the saliva of 100 children aged three to six across five kindergartens in Kerman. The average hand count rose from 1.85 particles on arrival to 4.2 on leaving. Most particles were under 100 micrometres.
Swallowed
Emerging evidence
What changes it. Hand to mouth is the route that matters most for small children, and a sink sits between the two.
Sources:
Amiri 2025
The plate and the glass
39,000 to 52,000
particles a year from food alone, varying by age and sex
Cox and colleagues pooled 402 data points from 26 studies covering about 15 percent of the American diet. Their estimate was 39,000 to 52,000 particles a year from food, rising to between 74,000 and 121,000 once inhalation is added. The authors call these likely underestimates.
Swallowed, Breathed
Strong evidence
What changes it. The drink is the sharpest contrast in their own data. Meeting the daily water intake from bottles added about 90,000 particles a year, against about 4,000 from tap.
Sources:
Cox 2019
The skin
1.6 to 2.0 percent
of one flame retardant came off the particle in a lab test standing in for skin contact
Abafe and colleagues ran a lab test, with no living skin involved, of what comes off microplastics carrying brominated flame retardants when they sit against a stand-in for the skin surface. Between 1.6 and 2.0 percent of the applied dose of one retardant came off in a form skin could take up. What came off in this test was the additive chemistry, not the particle.
Through skin
Modelled evidence
What changes it. Cosmetic formulations on the skin changed how much came off the particle. That is a result in a dish, not a rule for a bathroom shelf.
Sources:
Abafe 2023
What nobody has measured
Whether a whole particle crosses intact skin. The work so far measures the chemistry that comes off a particle, or uses cell models. Nobody has counted particles that made it through living skin.
