Pee Foam

Anyone who has used a urinal has probably seen the phenomenon: the urine foams up at the bottom of the receptacle like the world’s worst cappuccino. Why? Is it a chemical component of urine that causes it? It doesn’t foam the same way when going in a standard toilet. Is it the physics of urinal design? Inquiring minds…

Urine normally contains modest amounts of proteins (high levels indicate kidney problems). Protein molecules are long chains which, ordinarily, are curled up into tiny balls. The balls are small, and in low concentration don’t change the behaviour of the fluid much.

However, vigorous physical stirring will tend to bash these balls open, so that they unfold to a certain extent, or even entirely. Now these molecules form very long thin threads, and these threads can tangle up with each other, and thereby change the behaviour of the fluid, for example allowing small patches to become much more viscious (slow moving), so that air pockets that momentarily form in the fluid break up and collapse (which requires the flow of water typically through the narrow channels between the bubbles) much more slowly. Hence, air bubbles die much slower, which you see as foaming. (The air bubbles are themselves initially formed by the collision of the stream with the standing pool, the foam appearance comes because these air bubbles do not essentially immediately dissipate.)

Essentially the same phenomenon underlies beating egg whites, only egg whites contain much high concentrations of protein, so the foam that forms can be much denser and longer-lasting. It’s the same idea, however: the physical beating unravels the proteins, which then form sticky threads that change the flow properties of the fluid.

Speak for yourself!

I did not expect such a thorough answer so quickly. Of course, this being the Dope, I should have. Thanks!

My pee foam is like meringue? Yum.

Pee foam in the toilet was my first exposure to the concept of continental drift.

[John Denver]
Pee foam, in my toilet, makes me happy;
Pee foam, on my shoe, makes me cry…

You’ll never look at a lemon meringue pie the same way again…

I was thinking I’d never look at a lemon meringue pie again.

Nice answer, Carl Pham. And, in 10 minutes!

In this old thread on the same question, there was a minimally informative answer in 11 minutes. We’re getting better it seems.

A bunch of years ago my wife told me about a medical problem that one of her (female) co-workers was diagnosed with, and that she was led to know there was a problem because her pee had foam on it. I was incredulous - pee always has foam on it!

My wife informed me that men’s pee always has foam on it, but if a woman’s does, it indicates a medical problem. I’ve since assumed that foam on men’s pee is a function of some protein that gets added by the prostate.

So urine does not contain trapped gasses? I always assumed it did, and that’s what was filling up the bubbles created by the proteins.

Normal amount of protein in urine is under 10 milligrams/decilitre. That’s very little. (Egg white has about 6600mg/dl for comparison. And even that only foams well if you can keep the yolk out.) Is that really enough protein to form the colloids that create foaming bubbles? I don’t have a better answer but I am not so sure I can buy that explanation as sufficient by itself. I think there must be something more to the answer. Maybe the acidity and/or other ions contribute to the ability of the protein to denature (unwind) in urine?

Anyway, the other part of the question is why in the urinal and not in the toilet? Two reasons: one the water in the regular toilet dilutes whatever the constituents are even less, and two, the shape of the urinal surface pushes more air under the surface stream than dropping into a flat surface does.

Tossed off a pee-foam explanation without batting an eyelash.

You, sir, are a god in my eyes.

Seriously. Not only did I get an explanation, I got a link to a previous discussion on the same obscure topic. :cool:

What do you mean? Bubbles happen with peeing in both places. Is that not everyone’s experience? I remember when I was younger I took it as a challenge to have the surface of the toilet water covered with bubbles by the time I finished going!

Well, not mine, and not in the op’s either.

I might’ve gone with “Pee Foam Alabama.”

My toilet pee isn’t bubble-less, but it’s nowhere as foamy as my urinal pee.

I asked the same question almost ten years ago. heh.