ABCC11

In one line: A single letter in the gene ABCC11 decides whether your earwax is wet or dry, whether your armpits can make body odor, and which microbes live on your skin — and that one letter traces a map of human migration.

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The gene

ABCC11 sits on chromosome 16 (band 16q12.1). It encodes an ATP-binding cassette transporter — a microscopic molecular pump — that works inside your apocrine glands, the specialized sweat glands that line your ear canals, your armpits, and your breasts. At one position in the gene (base 538), people carry either a G or an A. That single nucleotide polymorphism — rs17822931, which swaps amino acid Gly180 for Arg180 — turns out to control a surprising amount of everyday human biology.

The hunt

The switch was identified in 2006 by Koh-ichiro Yoshiura, Norio Niikawa, and their colleagues at Nagasaki University in Japan. They genotyped more than a hundred volunteers — some with wet earwax, some with dry — and scanned their genomes, first narrowing the signal to a small pericentromeric region of chromosome 16, then to a handful of candidate genes, and finally, across 37 SNPs, to the single base in ABCC11. People with dry earwax were all homozygous for one allele, exactly as expected for a recessive Mendelian trait. It was the first time a single letter of DNA was shown to determine a visible, everyday human trait — earwax type is now a classroom example of a one-SNP phenotype.

The mechanism

Why does one letter matter so much? The G version of the gene builds a working pump. The A version changes a single amino acid in the protein, and that change has a drastic consequence: the variant protein lacks an N-linked sugar tag it should carry, so the cell's quality-control machinery reads it as misfolded and destroys it by the ubiquitin–proteasome pathway (ER-associated degradation) before it ever reaches the gland. No pump means nothing gets secreted. Inherit two A's — one from each parent — and you get dry earwax; a single working G is enough for wet, which is dominant.

The smell, and the microbiome

The pump's second job is your body odor. Fresh apocrine sweat is completely odorless. The working pump secretes invisible, scentless precursor molecules onto the skin, where bacteria take over: skin commensals — notably Staphylococcus hominis, using a Cys-S-conjugate β-lyase (PatB) — cleave the precursors into the volatile thiol (3M3SH) we recognize as body odor. The smell, in other words, isn't really made by you; it's made by your microbes feeding on what the pump puts out. Break the pump (the A/A genotype) and the bacteria lose their substrate — and there's almost nothing to smell.

Because the pump sets the chemical "menu," it also shapes who lives on you. Armpits of people with the working allele are dominated by odor-making Staphylococcus; those without it shift toward Corynebacterium and other microbes. The same genome–microbiome interaction shows up deep in the ear canal, where wet-wax and dry-wax ears grow measurably different bacterial communities.

The map

That one letter also draws a map of human history. The dry-earwax A allele arose in northeast Asia, perhaps ~40,000 years ago, and spread along a geographic gradient that peaks in Korea and northern China. Today it's carried by roughly 80–95% of East Asians — and by almost no one (≈0–3%) of European or African descent, where wet earwax and body odor are nearly universal. It's part of why the deodorant aisle looks so different around the world, and why, in Japan, strong body odor (axillary osmidrosis) is a recognized medical condition — historically diagnosed, in part, by checking a person's earwax.

Sources

Full claim-by-claim evidence is in references.md. Primary anchors:

• Yoshiura et al. (2006) — A SNP in the ABCC11 gene is the determinant of human earwax type. Nature Genetics 38, 324–330. (the discovery)
• Toyoda et al. (2009) & Ishikawa, Toyoda, Yoshiura & Niikawa (2013) — the proteasomal-degradation mechanism and a full review by the discovery team. FASEB J / Frontiers in Genetics.
• Stevens & Roesch (2024) — the armpit microbiome / 3M3SH body-odor pathway. Scientific Reports.
• Amari et al. (2025) — the ear-canal microbiome differs by ABCC11 genotype. Microbiology Spectrum.
• Ohashi, Naka & Tsuchiya (2011) — the age and selection history of the allele. Molecular Biology and Evolution.

Accuracy note: The earwax literature (including the 2006 discovery) names this variant 538G>A (G = wet, A = dry). NCBI dbSNP lists the same variant on the opposite DNA strand as c.538C>T (C = wet, T = dry). They are identical — same SNP rs17822931, same amino-acid change Gly180Arg, same direction (ancestral wet → derived dry); they differ only by which strand is read. This episode uses the G/A convention throughout.