Did you know that there are two types of earwax and that, depending on where you are from, you have one or the other?
Earwax, also known as cerumen, is produced by glands in the ear canal. It’s actually a mix of secretions from two different types of glands to which skin flakes, dust and debris get added. Its function is debated, but it probably acts to trap bacteria and insects and to keep the ear canal lubricated. Earwax moves out of the ear according to a conveyer belt mechanism: skin cells inside the ear transport it out by migrating out of the ear at a rate of 1/20th of a millimetre every day, similar to the speed at which our nails grow.
The vast majority of people of European or African descent have wet earwax. Like honey, it is yellow and sticky. Most East Asian people, however, have dry earwax, which is grey, brittle, and non-sticky. The landscape becomes much more muddied, however, when looking at people from the Pacific Islands, South and Central Asia, as well as Indigenous populations of North America, where 30 to 50% have dry earwax types.
By looking at families, we’ve known for a while that wet earwax was inherited in a dominant fashion. We receive two copies of most genes, one from our mother and one from our father. A dominant trait like wet earwax means that as long as a person has one copy of the wet earwax gene, they will produce wet earwax. They could have received a copy from their mother or from their father or from both: their cerumen will be yellow and sticky. To make dry earwax, they would need to receive the dry earwax version of the gene from both their mother and their father.
The gene that determines the type of earwax the body produces was identified in 2006 after a big clue to its location had been observed four years prior. A Japanese woman presented with a rare disorder, whose name will delight fans of Scrabble: paroxysmal kinesigenic choreoathetosis. It means she had brief episodes of involuntary contractions and twisting and writhing of her arms and legs. Six other people in her family also had these symptoms, which suggested a genetic origin. That, in and of itself, is unremarkable. The curious thing was that this rarity was not limited to the choreoathetosis: they also all had wet earwax, which is very uncommon among Japanese people.
Two rare genetic traits affecting the same people in a family? It probably meant that both genes were close together on the same chromosome, because the frequent DNA recombinations that occur during the making of sperm and eggs would have separated them otherwise.
A team of Japanese scientists used this knowledge to map the earwax gene to chromosome 16 and a few years later they found the exact gene that was responsible for the consistency and colour of someone’s earwax. In a world in which genetics can be extremely complicated, what the researchers found was the simplest possible explanation: a one-base change—a single-letter change in the A, C, T, G alphabet of the DNA molecule—was responsible. People who had a G at a specific spot in this gene produced wet earwax, and those with an A on both copies of the gene made dry earwax. It was that easy.
The more interesting question is why. DNA makes proteins, and this particular stretch of DNA, a gene called ABCC11, codes for a protein called a transporter. In people with wet earwax, this transporter protein can be found inside the glands that produce some of the secretions present in earwax, and it helps with the release of these secretions. But in people with dry earwax, the protein cannot bind to a particular sugar. It is seen as defective and the cell breaks it down before it can fulfill its role.
Seen through this molecular lens, you may think that people who have dry earwax are “defective” in some way but that is not true. Dry earwax in itself does not seem to create any problem. In fact, this one-letter change in the DNA code for the ABCC11 gene has a pleasant consequence: less stinky sweat. Indeed, some of the same glands involved in producing earwax secrete sweat elsewhere in the body. People with wet earwax not only release smelly compounds in their cerumen thanks to the ABCC11 transporter protein: they also release smelly compounds through their armpit sweat, a trait known to Scrabble players everywhere as axillary osmidrosis.
The mechanism is simple. In both wet earwax and its corresponding armpit sweat, ABCC11 transports certain natural molecules out of cells, and bacteria on the skin feast on them, transforming them into smelly, volatile organic compounds. Scientists have used gas chromatography/mass spectrometry to identify these compounds in both wet and dry earwax and, sure enough, they found larger quantities of them in the earwax of white volunteers compared to that of East Asian participants.
Earwax may be gross but the scientific discoveries surrounding it could lead to diagnostic applications. A molecule called sotolone causes the sweet smell found in maple syrup urine disease, in which some of the building blocks of proteins found in food can’t be broken down, and sotolone can be detected in the earwax of infants who have this condition. The SARS-CoV-2 coronavirus can also sometimes be detected in earwax samples from patients with COVID-19. But more interestingly, a problem with the inner ear called Ménière’s disease, in which people experience vertigo and hearing loss, is typically diagnosed by excluding everything else; but a team in Albany, New York recently reported that the earwax of these patients has lower levels of three fatty acids. Interrogating cerumen samples with a mass spectrometer may one day help doctors more quickly diagnose patients with this condition.
As for what to do with earwax, the answer is to simply leave it alone until it makes its way out of the ear canal. Forcing a Q-tip down the canal can actually push earwax further down and compact it, which can affect hearing. It can even tear through the eardrum. Unless it is causing problems, we should simply let the earwax be, whether it is wet or dry.
Take-home message:
- Earwax can either be wet or dry, which is decided by a single letter change in a gene called ABCC11
- People of European or African descent tend to have wet earwax, whereas most East Asians have dry earwax
- Because the protein made by ABCC11 is responsible for secreting molecules that are metabolized by bacteria into smelly compounds, people with wet earwax also produce armpit sweat with a more pronounced smell
