The Verification Venue · a number that changes with the method
The Census on Your Face
In the pores of your face live mites called Demodex — real animals, about a third of a millimetre long, almost certainly there right now. But ask how many people have them and the honest answer is: it depends entirely on how you look. Look with a microscope and you find them on 14% of adults. Look for their DNA and you find them on 100%.
Both numbers come from the same 2014 study — same researchers, same kind of facial samples. Counting mites by eye undercounts them massively; screening for their genetic signature catches what the eye misses. Pick a way of looking below, and pick who you're looking at. The prevalence is recomputed live from the study's own raw counts — and so is the confidence interval that the tidy headline "100%" quietly hides.
How do you want to look?
Who are you looking at?
Carry Demodex
13.8%
35 of 253 · inferred
95% confidence interval
13.8%
–
Wilson score interval
Counting mites under the microscope, the paper reports 14% of adults positive. The exact positive count isn't published, so 35/253 is inferred to land on that 14%. Now switch to the DNA screen and watch the same kind of samples tell a different story.
The gap between the two ways of looking
The lesson underneath the toggle is the point of the whole study: Demodex mites are "universal associates of adult humans." The visual survey isn't wrong so much as near-sighted — most people carry too few mites, too deep, to be caught by eye. The DNA screen finds the trace they leave behind. But the flashy "100%" deserves its asterisk: it is a point estimate on 19 people. With 19 positives out of 19, the true rate could still honestly be as low as the low-to-mid 80s — which is why the confidence interval is on the panel, not buried.
The check — every number recomputed from the raw counts
Percentages are computed live in your browser from the numerators and denominators printed in Thoemmes et al. 2014. The green column is the arithmetic, not a claim. One row is flagged reported: the 14% visual figure is quoted from the paper, which does not publish the exact positive count, so its numerator (35) is inferred to reproduce the stated 14% — it is reported, not derived.
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The honest floor under the headline 100% (19 positives, 19 tested), three ways:
The age-with-prevalence rise (roughly 13% in children up to near-100% in the elderly, ~35% pooled worldwide and ~59% past 60) is context from the broader literature, not from this 19-and-10-person study — flagged reported above and sourced below. Run every arithmetic check yourself: node research/mites-that-live-on-your-face/verify-mites-that-live-on-your-face.mjs.
What's proven, what's assumed, and what we couldn't verify
Proven (recomputed on this page and by the verifier). From Thoemmes 2014's published counts: DNA detection in adults over 18 = 19/19 = 100.0%; in 18-year-olds = 7/10 = 70.0%; across everyone DNA-tested = (19+7)/29 = 26/29 = 89.7%. The method gap between the DNA screen (100%) and the visual survey (14%) is 86 percentage points, a ratio of about 7.1×. The confidence floor under 19/19 is the low-to-mid 80s (exact binomial one-sided 95% lower bound 0.05^(1/19) ≈ 85.4%; rule of three 1 − 3/19 ≈ 84.2%; Wilson two-sided lower bound ≈ 83.2%).
Reported, not derived. The 14% visual prevalence is quoted verbatim from the paper as "14% (n = 253)"; the exact positive count is not published, so the 35/253 shown here is inferred to reproduce 14% (35/253 = 13.8%; the true count lies in the 35–36 range that rounds to 14%). The global pooled prevalence (~35%, peaking ~59% past age 60) is from a separate 2025 meta-analysis, and the age gradient (~13% in children to near-100% in the elderly) is compiled from review literature — neither is computed from Thoemmes 2014.
The correction to the popular framing. The famous "100% of people 18 and over" is, in the paper, 100% of people strictly over 18 (n=19); the 18-year-old bin was 70% (7/10). So the true claim is "essentially every adult," carried by molecular detection, not "literally everyone by any method."
What we couldn't verify. The exact visual positive count (hence 35 is an inference); the two mite species split (D. folliculorum vs D. brevis) is real but not recomputed here; and no microscope demo on this page is the check — the sourced prevalence arithmetic is. A DIY eyelash-under-a-lens look is illustrative only, and results vary wildly with technique, which is exactly the undercount the DNA method exposes.