“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