Pharyngula

i-ccbc028bf567ec6e49f3b515a2c4c149-old_pharyngula.gif

Not all the email I get is from cranks and creationist loons. Sometimes I get sincere questions. In today’s edition of “Ask Mr Science Guy!”, Hank Fox asks,

I was thinkingrecently about the fact that wax collects in one’s ears, and suddenly thought to be amazed that some part of the HUMAN body produces actual WAX. Weird. Like having something like honeybee cellsin your ear.

And then I started to think about what sorts of other … exudates the humanexterior produces.Mucus, possibly several different types (does the nose itself produce more than one type?).Oils, possibly several different types. That something-or-other that hardens into yourfingernails. Saliva, if you wanted to count our frequently-open mouth as sort-of exterior. What else?

Of course I know something about this subject, having taught physiology for a few years. My years of experience have also led me to notice that it is always the guys who ask about disgusting secretions. Why is that?

Anyway, fingernails (and hair) are not secretions. They are composed of interlocked, dead cells packed internally with high concentrations of the protein keratin. So let’s forget about those, and concentrate on the really yucky stuff instead: ear wax and another important kind of goo, smegma.

First of all, it’s not at all unusual that we would secrete a wax. What’s the difference between an oil, a fat, and a wax? Nothing but the melting point. All are esters (the products of condensation reactions between carboxylic acids and alcohols) with an aliphatic chain of carbon molecules. The length of the chain determines the volatility of the molecule; short chains are more fluid, long chains more solid. Something like olive oil will have shorter chains than something like beeswax, but all are fundamentally similar. They are all classified as lipids.

So earwax isn’t that unusual—it’s a compound on a continuum of perfectly normal lipid products produced by cells.

So what, exactly, is in earwax, or cerumen? Here’s where it gets ugly. It’s a combination of things:

  • Desquamated keratinocytes. Dead skin cells, in other words, that have peeled off of the epithelia lining the ear canal.
  • Sebum. This is an oily substance produced by the sebaceous glands that are scattered over most of your body. If you don’t wash your hair for a few days, you know that oily, greasy substance that builds up? That’s sebum.
  • Various waxes. The dense, waxy part of cerumen is a secretion from specialized glands in the ear canal, the ceruminous glands.

All of these combine into a greasy paste that helps protect the passageway into the ear from invaders. I know I wouldn’t want to set foot in it.

For a more detailed analysis of the chemical composition of ear wax, one can do a little chromatography. About half of the dry weight of ear wax is lipid, and it consists of:

Everyone with a little biology or chemistry background will recognize these as quite ordinary products of cellular metabolism. Also, these particular compounds are found in similar concentrations in another place: the stratum corneum, or outer layer, of your skin, where the fats and waxes and oils are secreted in a layer that surrounds the cells, providing waterproofing and lubrication.

While rummaging around in the files, I also found an older paper (from 1947) that analyzes another similar substance: smegma. As you might expect from the fact that it is also a waxy, oily secretion from skin cells, it is also about half lipid, and consists of:

  • Cholesterol and cholesterol esters: 18%
  • Fatty acids: 71%

This paper is notable for a couple of things. It tells us where to get a supply of smegma.

Smegma is best obtained from dead horses in rendering plants or from anesthetized animals in a department of veterinary surgery.

That’s good to know; I wouldn’t want to make the error of trying to collect smegma from live, conscious horses.

The other distinctive thing about the paper is that it is one of the more disgusting experiments I’ve read about. The authors were testing the potential carcinogenic effects of smegma, and the experiment involved making up slurries of smegma and smearing it or injecting it into folds of skin on mice, and assessing their health. It had to have been a big job, slathering 400 mice with smegma every week, and treating another 400 control mice with ear wax.

This study found an increased frequency of various cancers in the treated mice: 57 smegma-smeared mice developed various kinds of cancer, versus only 12 of the controls. Before everyone gets all worked up into the circumcision debate, though, I’ll mention that the paper is one of many that have tested this kind of thing, they acknowledge that other researchers have seen no carcinogenic effect, and that more modern papers suggest that there are no special carcinogenic properties of smegma. The paper shows another curious result, that the authors didn’t even discuss:

There was no significant difference in the survival rates of treated and control mice up to the 400th day of life: 85 and 88 per cent, respectively, after 200 days; 74 and 80 percent after 300 days; 65 and 57 percent after 400 days. After 500 days, 47 percent of those treated with smegma were alive as compared with 30 percent of the controls. From the 600th day on, there was a marked difference (26 and 6 percent, respectively), and on the 700th day, the survival rates were 12 and 1½ per cent.

Personally, I think the smegmated mice were just so pissed off that they kept going out of infuriated spite.

By the way, Hank also asked about mucus, but I think I’ll save the discussion about snot for another day. Right now, it’s time for me to go to lunch.


Bortz JT, Wertz PW, Downing DT (1990) Composition of cerumen lipids. J Am Acad Dermatol 23(5):845-9.

Plaut A, Kohn-Speyer AC (1947) The carcinogenic action of smegma. Science 105(2728):391-392.

Comments

  1. #1 Jerry
    June 11, 2006

    I know I’m being picky, but you are wrong in a number of things (I consider this important since you say you used to teach physiology)
    1) Nail composition does not include dead cells. Neither does hair. It’s only keratin. The stratum corneum does include dead keratynocytes, tho. and…
    2) (the one that bugs me the most) – The MAIN difference between oils and fats is not the chain size. Even tho it’s true that smaller chains make for a more fluid lipid, vegetable oils and animal fats are mostly long chain lipids (ie, more than 10 carbons). The main difference, and the one that mostly determines their melting point and viscosity is the amount of insaturations said chain has. Oily lipids have the most insaturations (often one every other carbon atom), while the heaviest waxes and fats have one, or none.

  2. #2 David Harmon
    June 11, 2006

    While I can’t speak regarding smegma, wearing hearing aids has given me some familiarity with earwax (gotta clean those things). One amusing thing I’ve discovered is that the stuff is explosively flammable. Torching a glob (usually on a paperclip) yields a burst of white flame before it settles down and burns to a tiny ash.

    I’m sure that similar experiments are behind the urban legend about people’s earwax building up and catching fire in their ears. (Reality check: any such fire would be short on oxygen due to cramped quarters, and would also be “arguing” with the water in surrounding flesh and blood.)

  3. #3 David Harmon
    June 11, 2006

    I just wandered through the “taste of Pharyngula” sidebar to find “the proper reverence for those who have gone before”. That would be a great article to bring forward as a repost!

  4. #4 Polly Anna
    June 11, 2006

    Oh my goodness, thank you Mr. P.

    I love articles about “Grease,” your article though a small aspect, grease is the basis of the evolution of man and progression of her culture to date.

    I know you are vertebrate-centric (invertebrately-challenged?), but grease is nature’s storage depots for solar energy beginning with the lowest up through the highest organisms, plants perhaps the most efficient, fossil fuels the best example of greatest impact.

    What with a global warming cycle coming, we should examine this closer and exploit it more.

    Polly A.

  5. #5 John Pieret
    June 11, 2006

    Right now, it’s time for me to go to lunch.

    If this was talk.origins, I’d have to say “That snot funny!”

    But since it isn’t . . .

  6. #6 Abie
    June 11, 2006

    I loved it first time I read it, but it begs for a milder question : what about saliva?
    What’s in it besides amylase? what gives it its slighty viscous feeling and lubricating property?

  7. #7 The Countess
    June 11, 2006

    I must be a dude. I like anything with a high spooge factor. I even watched a movie called “Slugs” once just because I liked the title. I had hoped for ick, and I got it.

    A couple of nights ago, I really got under The Count’s skin by reminding him in gory detail about all the dust mites that were munching on his dead skin cells in our bed. He started to itch. A lot.

    What a great way to start a Sunday. Read a post that includes stuff about smegma. I already told The Count that you wrote a post that has stuff about smegma in it. He’ll definitely be by later today… 😉

  8. #8 _PK_
    June 11, 2006

    I didn’t recall ever seeing the word “smegma” before, so I used my right-click function to look it up at the FreeDictionary.

    smeg·ma – A sebaceous secretion, especially the cheesy secretion that collects under the prepuce or around the clitoris.

    I gotta talk to my wife about this

  9. #9 ulg
    June 11, 2006

    what about saliva? What’s in it besides amylase? what gives it its slighty viscous feeling and lubricating property?

    I don’t know anything about the chemistry, but there’s an evolutionary explanation for the lubricating property – relatively few men’s genitalia could survive adolescence without it. (Remember, hand lotion postdates the cultivation of oil palms, circa 10000 BP.)

  10. #10 woofsterNY
    June 11, 2006

    Re: lubricating property of saliva …

    I know this will sound strange, but I was once licked by a grizzly (long story) from fingers to elbow. The saliva dried almost instantly, and was non-sticky, but when I tried to wash it off with water a few minutes later, it turned into a persistent slime that took several minutes, and vigorous scrubbing, to wash off.

  11. #11 alane
    June 12, 2006

    My years of experience have also led me to notice that it is always the guys who ask about disgusting secretions.

    I can’t speak for all women, of course, but I’m personally kind of indifferent. Although now that I’ve read your post, earwax is kind of interesting.

  12. #12 bernarda
    June 12, 2006

    This is a little off on a tangent, but it does deal with body chemistry. Feces usually manage to slide out of the is it jinternal tubing without much problem. Yet once in the ceramic toilet bowl, it becomes very adhesive. If you don’t clean it regularly, it becomes firmly fixed to the ceramic surface, which however is designed to have things slide off it.

    What is the chemistry that makes feces become such a good glue? Also, has anyone tried to find out if there is a commercial product that can be synthesized out of it?

    Some time ago I asked this question to The New Scientist question page but never got a response. So, maybe it is just a silly question.

  13. #13 David Harmon
    June 12, 2006

    Bernarda: I suspect that would be the bacteria. Unlike dead blood cells, undigested food, etc., many bacteria have an active interest in attaching to surfaces. Note that despite appearances, most ceramics are somewhat porous even before wear-and-tear, so they have plenty of microscopic “handholds”.

    Once they’ve taken hold, they can multiply into a biofilm (that orange/brown slime). The biofilm not only sticks to the surface beneath it, but also “grabs” bits of passing “stuff”, thus making your toilet bowl progressively nastier.

    Eventually, of course, you trump their mini-ecology by invoking your own far-greater mass and strength (scrub scrub), not to mention blasting them with caustic chemicals such as ammonia or bleach.

    Note that the main reason we use ceramic tiles and basins isn’t so much that “things slide off”, as that (1) bacteria can’t get too deep into the surface (cracks notwithstanding), and (2) the material can survive drastic cleaning methods.

  14. #14 bernarda
    June 12, 2006

    Thanks for the info David. Is there any element in all that that could be commerically exploited?

  15. #15 Bill Dauphin
    June 12, 2006

    “One amusing thing I’ve discovered is that the stuff is explosively flammable.”

    So much for Shrek’s candles, eh?

  16. #16 Aaron Denney
    June 12, 2006

    I don’t know anything about the chemistry, but there’s an evolutionary explanation for the lubricating property – relatively few men’s genitalia could survive adolescence without it. (Remember, hand lotion postdates the cultivation of oil palms, circa 10000 BP.)

    Intact male genitals don’t need nearly as much lubrication. And circumcision hasn’t been going on that long, nor that widespread.

  17. #17 CortxVortx
    June 12, 2006

    > smeg·ma – A sebaceous secretion, especially the cheesy secretion that collects under the prepuce or around the clitoris.
    >

    And here I was thinking that the female counterpart to smegma was “Vulveeta.”

  18. #18 ArtK
    June 12, 2006

    I wouldn’t want to make the error of trying to collect smegma from live, conscious horses.

    Happens every day. If you own a male horse, you have to “clean the sheath” regularly. This is a real problem for geldings since they don’t “drop” as often as stallions, so the stuff doesn’t rub off.

    Method: Soak soft rags in a mild soap solution and, um, shove them up around the penis and sheath. Then remove them and repeat with clean, unsoapy rags. Tranquilizers are often recommended, both for the horse and the care-giver.

  19. #19 PZ Myers
    June 12, 2006

    I’m imagining every horse owner regularly downing a couple of shots of whiskey before heading out to the barn to fondle the beast.

  20. #20 RavenT
    June 12, 2006

    Maybe *that’s* what they were really doing in Enumclaw…or so they may want to claim, anyway.

    (Mr. Raven has a student from Enumclaw–apparently, he says, the community is not too happy about their recent notoriety as the horse sex capital of the U.S.)

  21. #21 David Harmon
    June 13, 2006

    “Is there any element in all that that could be commerically exploited?”

    Certainly… of course, cleaning products are already a massive industry, so the competition is pretty stiff….

  22. #22 Andrew Wade
    June 13, 2006

    Note that the main reason we use ceramic tiles and basins isn’t so much that “things slide off”, as that (1) bacteria can’t get too deep into the surface (cracks notwithstanding), and (2) the material can survive drastic cleaning methods.

    I thought it was to simply dessicate any germs on the surface. Hence my amusement whenevery anyone compares the number of bacteria found in various places to the number found on toilet seats. (Plus, there’s nothing necessarily wrong with bacteria in the first place).

  23. #23 mps
    September 7, 2006

    You claim it’s only guys who ask about stuff like smegma and earwax, and I’m here to tell you, you’re dead wrong. Women talk about that stuff all the time, too – just not to guys. Anaconda all that social pressure to appear “dainty” and “feminine,” and all that, yknow.

    mps
    “My idea of feminine protection is a pearl-handled revolver”

  24. #24 Marcus Ranum
    July 16, 2007

    “I wouldn’t want to make the error of trying to collect smegma from live, conscious horses.”

    I have 2 geldings and – believe me – it’s periodically necessary to get up in there and give them the old smegma removal wipe-down. They can, depending on the horse, produce quite a lot of the stuff. It’s, um, really daunting.

    I suspect other male animals (rhinos? elephants?) probably also produce massive quantities of the stuff, but believe me, it’s bad enough getting a horse to stand still while you reach up into his sheath – a rhino would probably a once in a lifetime experience.

  25. #25 Onkel Bob
    March 14, 2008

    Someone has to say it..

    “You think it’s butter but it’s snot…”

  26. #26 Felipe Budinich
    March 25, 2008

    “One amusing thing I’ve discovered is that the stuff is explosively flammable.”

    Got to remember that when trying to start a camp fire.

    “Is there any element in all that that could be commerically exploited?”

    Theres already people developing paints that use the same principle, like a kind of white moss that’s being used to paint roads, they only got to paint once, and it regenerates the damage caused by traffic.

  27. #27 Kenny P
    July 8, 2008

    I always thought Smegma was the ugly Gabor sister that neither Madga, Zsa Zsa, or Eva never talked about. Am I wrong?

New comments have been temporarily disabled. Please check back soon.