“Mommy, why do I need to wash my hands if I only pee?”

by Gillian Mayman on September 24, 2012

An illustrated guide to parenting with science.

I have three boys. Two are generally filthy and one is very clean.

The filthy ones rarely wash their hands after using the bathroom at home, if all they do is pee.

One of the lessons that they’ve learned from watching wilderness survival shows on TV (e.g., Man vs. Wild, etc.) is that pee is sterile and safe to drink.

Based on this information, they argue that washing your hands after peeing is like washing your hands after drinking apple juice.

Their argument is based on the idea that urine is sterile. If you check Wikipedia, WebMD,  and almost every other web page, you will find this stated as a fact.

It turns out, however, that this idea is a myth.

Like a unicorn.

Or the idea that your entire house is not teaming with bacteria.

Researchers from Loyola University Chicago (and a few other institutions) found that urine is not, in fact, sterile. It contains bacteria even when it is still in the bladder.

The researchers collected urine using voided, transurethral, and/or suprapubic collection methods from women with no current UTI (that’s Urinary Tract Infection, for those lucky enough to not know).

In other words, the women peed in a cup, had a catheter threaded up their urethra and into their bladder, and/or had the urine collected by a needle inserted through their abdomen and into their bladder. This is important because they needed to make sure that the urine was not being infected with bacteria outside of the bladder.  Urine is known to become infected as it exits the body and comes into contact with bacteria at the opening of the urethra.

When bacteria was found in the urine, it was assessed by bacterial culture, light microscopy, and 16S rRNA gene sequencing.

Bacteria was found in the majority of the samples taken, although most of the bacteria could not be detected using common clinical laboratory procedures. Even in samples taken through suprapubic catheterization, 21 out of 23 samples were found to contain bacteria.

(This also has the inverse finding of 2 samples not containing any bacteria, indicating that some urine is, in fact, sterile.)

A new argument for my boys might be:

The concerns about what splashes out the the toilet when you flush it and the amount of bacteria that is encountered when touching the toilet handle, the sink, and the bathroom doorknob will have to wait for another argument.

Wolfe, A. J., Toh, E., Shibata, N., Rong, R., Kenton, K., Fitzgerald, M., . . . Brubaker, L. (2012). Evidence of uncultivated bacteria in the adult female bladder. Journal of Clinical Microbiology, 50(4), 1376-1383. doi: 10.1128/JCM.05852-11

Tim Jones September 24, 2012 at 9:05 am

Great post. Love posts about toilets, bodily fluids, and generally speaking the unspeakable.

It’s always struck me as odd that we don’t see signs in toilets advising us to wash our hands BEFORE taking a pee – boys and girls. i.e. toilet door handle = bacteria, stuff you were doing before peeing (gardening, working on car, developing bio-weapon) = bacteria, therefore was hands before peeing.

I’m also fascinated by those little plastic grates they insert in urinals to reduce splash; I patented something similar once for use with liquid steel :-)


Carol Shannon September 24, 2012 at 9:30 am

Great post, Gillian! It’s well written and amusing (always good). I love the graphics. I only have a small quibble: a couple of times you use some language that is a bit technical for the general public (i.e., “inverse finding”).

Looking forward to reading more!

Gillian Mayman September 24, 2012 at 3:00 pm

Thanks, Carol :)

I did struggle with how simple to make the language. It seemed that when I made the language simple and accompanied the text with the child-like illustrations, it just seemed too… simple. I’ll keep trying to find a better balance.

anna September 24, 2012 at 9:38 am

Very instructive while also being entertaining! Thank you, Gillian. On the subject of peeing, I do want to add for the record that I hate when the toilet (like the ones found in airports, restaurants, etc.) flushes ME–I would rather flush IT.

Robert September 24, 2012 at 10:07 am

I’m waiting for the “another argument” because from a realistic point of view, outside my home, i do not wash my hands after pee:
1) A male can pee without any urine transfer to the hands
2) A male can pee by only touching clothing, not flesh
2) Anything touched in the bathroom is extremely dubious
3) A touch free experience: flush with foot and open door with paper towel or sleeve

Tim Jones September 24, 2012 at 12:38 pm

Technically possible. Folks who operate this way can be identified by their moldy shoelaces and rusty zips.

PGYx September 25, 2012 at 9:37 pm

The real problem is that your hands are already dirty from contact with the rest of the world prior to your bathroom trip. Washing your hands at regular intervals (e.g., each time you pee) is a great way to reduce transmission of organisms that cause colds and gastrointestinal illness — organisms commonly found on items like doorknobs, phones, and computer keyboards.

The other Robert October 2, 2012 at 11:03 am

Can you pee without touching your wang? Because unless you’ve just showered, that’s probably got way more bacteria than your urine does.

I don’t understand why these arguments are always about whether *urine* is sterile, when there’s a much more obvious source of contamination.

Quintus September 24, 2012 at 10:46 am

Great post. The pics are wonderful as is the subject matter. These depicted kids cannot ingest anything anyway, they have no mouths:))

Gillian Mayman September 24, 2012 at 3:01 pm

Very true! Wishful thinking on my part.

Margaret Freaney September 24, 2012 at 10:55 am

Nice post. I love the way you explained in easy language what transurethral and suprapubic meant. The accompanying illustrations made the whole medical terminology part of your post accessible to people with no medical background.

The only part that was not difficult for me, but might be for others is the symbol for “therefore” in you pictures. Your illustrations were great for any level of education other than that.

I look forward to more of your fun posts.


PF Anderson September 24, 2012 at 12:01 pm

I adore this post. Real world, relevant, personal, personable, clever, witty, amusing, colorful, excellent graphics, solid science. I assume you made the images yourself? Are you sharing them as Creative Commons images? Also, while I’m very grateful for the closing citation to the article discussed, I’d have also appreciated a link to the article, either at the journal or at Pubmed, as part of the citation. http://www.ncbi.nlm.nih.gov/pubmed/22278835 I was impressed by your choice of the DOI for the in-post link. Bravo! Most folk don’t know what a DOI is, and that is the best choice for longterm utility.

Gillian Mayman September 24, 2012 at 3:05 pm

Thanks, Patricia. All of the contents of this blog are under a Creative Commons license. I did create the images myself- it seemed easier than finding copyright free content and it also fit the kid-focused theme (luckily, I draw with the skill of a six year old).

I’ll update the citation to include a link.

PF Anderson September 24, 2012 at 12:09 pm

Showed this to my kid. Made him read it. I know, it wasn’t written for kids. He said the graphics are confusing, and there are too many big words that aren’t defined. Sigh.

Gillian Mayman September 24, 2012 at 3:06 pm

Good to get that feedback, thanks.

Shara E September 25, 2012 at 2:01 pm

I’d love to see what happens if you were to do a follow up asking each of your kids to explain why they are right and you are not , complete with their own illustrations. So much potential!

Tevah Platt September 24, 2012 at 1:48 pm

I love it! The pictures are super cute and fun.
I do have a question though… Is the bacteria in pee harmful?

Gillian Mayman September 24, 2012 at 3:02 pm

These researchers did not look at that, so we don’t know yet.

John Spevacek September 25, 2012 at 1:22 pm

That’s an ongoing rant I have with microbiologists: they find a bacteria, but never identify if there is enough there to be worried about. The whole concept of “it’s the dose that makes the poison” is alive in well in medicine, chemistry and physics, but not in biology.

Brian Zikmund-Fisher September 24, 2012 at 3:10 pm


If you want a followup topic, I’d actually really like to learn more about these waterless urinals that are starting to pop up in public restrooms. Are they really (a) hygienic, (b) odorless, (c) saving that much water?


Gillian Mayman September 24, 2012 at 5:22 pm

While choosing a focus for this blog post, I realized that I could write at least 50 posts on bathroom issues alone. That may have to wait for a separate blog, though!

Marie Kotenko September 24, 2012 at 7:14 pm

Thanks for posting images – I only had time to skim and felt like I got the idea!

Steen September 24, 2012 at 8:24 pm

If the bacteria are rare enough to not be detected via common clinical laboratory procedures, then I would make the argument that there is less bacteria in urine than there is on the bathroom faucet. Just sayin.

Jason September 24, 2012 at 8:25 pm

Love the illustrations!

Steve Jensen September 25, 2012 at 1:46 am

After little boy #1 starts to exit the boys’ room without hand washing:
Little boy #2: “Didn’t your Mother teach you to wash your hands?”
Little boy #1: “No. My Dad taught me not to pee on my fingers.”

I know it doesn’t help the argument. I just think it’s cute.

Maybe a better argument is that any opportunity to wash your hands, especially for children, should be grabbed.

Alison September 25, 2012 at 12:51 pm

Great post Gillian! I love the “parenting with science” tagline. More instructive than most parenting websites out there! I look forward to your next post.

Shara E September 25, 2012 at 2:11 pm

I love what you did with all of the images. They really do help illustrate your points, and are pretty hilarious to boot. I’m curious to know how the goat argument went over with your boys, any luck ?

Gillian Mayman September 25, 2012 at 2:20 pm

The goat example works with them because I’m a huge stickler for hand washing after petting farms. I tried to think of a more broadly applicable example but I thought goats were just funny. (This is not to say that they are better at washing their hands now- the example didn’t work that well!)

Bob September 25, 2012 at 7:08 pm

The Loyola study only shows that adult women have bacteria in their urine. As far as I can tell, men (and boys) are still good to go.

Pat September 26, 2012 at 2:06 am

The study shows that women should wash their hands because they have bacteria in their urine that may or may not be harmful.

My boys said too: confusing graphics.

And they may or may not wash their hands after peeing.

Nancy Linde September 26, 2012 at 9:12 am

Well done, but the message will be missed on those who assume the bacteria in their bodies are generally good. Maybe it would be more effective to have illustrations showing all they types of bad bacteria and viruses they could have picked up on their tiny hands in the hour preceeding the trip to the bathroom, as well as those in the bathroom. Then show how they can transmit those germs to others, especially if there’s a baby or immune compromised person in the house, or in their friend’s house…

Gerry September 26, 2012 at 9:15 am

Your credibility is lessened if you cannot use correct spelling. The word bacteria is the plural of bacterium. You use bacteria in the singular in your article. Shame.

Dabbe September 26, 2012 at 9:20 am

“most of the bacteria could not be detected using common clinical laboratory procedures” would suggest very low densities, wouldn’t it? Hence the culturing and sequence amplification?

So pee isn’t completely sterile but has probably less bacteria than any doorknob, chair, keyboard etc., there are probably more bacteria on your hands at any time than there are in your pee, I’m not saying you shouln’t wash up after, but it makes much more sense to wash up before.

Dabbe September 26, 2012 at 9:25 am

This means rinsing hands, doorknobs, etc. with (non-UTI) pee would (at least temporarily, but the same goes for water and soap) lower the bacterial densities of those surfaces.
Relatively sterile still stands!

Mary September 27, 2012 at 3:35 pm

Awesome post, Gillian! I guess I always found it hard to believe that there was any part of the human body that was actually sterile. Now I’d like to know about the bacterial count on the hands of people who do and don’t wash post-pee. If there’s no difference, maybe kids like yours (and mine) can still get a pass.

Jean Song September 28, 2012 at 2:30 pm

I really enjoyed reading this post, Gillian, considering the hygiene habits of my children! An interesting follow up study for me would be to test the urine of male subjects to see if there were similar results (and could possibly explain why my daughter consistently washes her hands after she uses the restroom but my son does not). :) Upon reading the article, it is interesting to note that the researchers could not determine whether or not the bacteria had been introduced to the bladder or existed in the bladder which would also be interesting to know perhaps for further insight into UTIs… Thanks for bringing up this really great topic!

Meadows2 September 28, 2012 at 5:43 pm

Very well done. I really enjoyed the details, the research and the practical application (i.e. how you might educate your sons and the world) of the findings.

Larry September 29, 2012 at 2:44 pm

I think the idea of washing your hands after urinating is backwards. You might want to consider when entering a public restroom as a man to wash your hands prior to urinating and then wash them again after. If the sink is not automatic turn off the sink with a paper towel after you wash your hands To further reduce the risk of contamination, use a paper towel to open the door to exit the restroom and throw the towel way either before you let the door close or afterwards. I emphasize the paper towel on the door handle part because if you ever watched people leave a restroom, a male restroom in my case, a significant number of people do not wash their hands at all regardless of which area of the bathroom they are exiting from. Gross.

Werner September 29, 2012 at 3:50 pm

An article that provoked lively discussion among my young adult offspring. Unfortunately, the cited study only included women, who have a urethral opening much closer to the bladder than men. I would be interested to know if the urine samples in men are more likely to be sterile? My take…ALWAYS wash your hands after bathroom duties of any kind to reduce exposure to the germs left by previous occupants – even if you never touched yourself or your own body fluids.

jif October 1, 2012 at 9:24 pm

Personally, I am more concerned about touching my penis with my hands that have been all over who knows what than what happens to my hands after I touch my clean penis with my filthy, filthy hands.

Best to ask your boys to wash BEFORE and AFTER!

Hibbleton March 4, 2013 at 8:16 pm

Ever heard of the ‘hygiene hypothesis’? Let me know if you still have the same point of view when your children get Crohn’s disease.

jonw April 30, 2013 at 1:25 pm

Ok this was educational reading, I did not know there are bacteria in urine. But there are also bacteria everywhere else, and presumably the ones everywhere else are well-adapted to living out in the fresh air, on skin, doorknobs etc. Is there something special about the bacteria in urine that should make me want to wash my hands, or is it just a cultural aversion, something along the lines of “urine is nasty, I better make sure no drops of it are still on me.”

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