Urinal Cakes: Why?

If you happen to frequent urinals, odds are you’ve seen one that has… a little block at the bottom of it. They’re often called “urinal cakes”, and a lot of urinals have them. But here’s a pro-tip for you. They’re not really cakes. So, why are they there? Well, the key is in the more proper-sounding name for these things. They’re technically called Urinal Deodorizer Blocks because that’s what they do. They make urinals smell a little less awful. Even though it doesn’t always seem to make much of a difference. Urine isn’t generally supposed to have a strong smell But it can depending on certain factors. Some foods like coffee or asparagus will often give pee a particular odor. And medical conditions like bladder infections or uncontrolled diabetes can also cause urine to smell. Then there’s the fact that urine contains ammonia The higher the concentration, the worse it smells. That generally happens when you’re dehydrated But when you leave urine laying around for a while Bacteria can start digesting some of the other main components of urine Mainly, urea and uric acid producing even more ammonia. So it isn’t too surprising that a urinal would smell not great. There’s a lot of pee going into that thing and not all of it necessarily ends up in the drain, even if the urinal flushes. Enter the deodorizer block. In the early days of urinal cakes, probably around the turn of the 20th century, the little slabs were mostly made of naphthalene, AKA, olden-day moth balls. The main thing naphthalene does is vaporize Making the air smell very strongly like mothballs and therefore a lot less like urine its also been shown to stop some bacteria from producing ammonia which might eliminate some of the stuff which is causing the odor in the first place. Today, you might still encounter urinal cakes with this stuff in it but it’s a lot less common. Probably, because too much naphthalene isn’t very good for humans when it is ingested it can destroy red blood cells and you need those Plus, according to the US Department of Health and Human Services, Naphthalene is “Reasonably anticipated to be a human carcinogen” So, peeing on the stuff every once in a while is probably okay but you wouldn’t wanna get any closer to it than that. Many urinal cakes these days are made of a compound called a molecule that looks a little bit like a throwing star and is often used as a naphthalene replacement in moth balls. That’s because, like naphthalene, paradichlorobenzene has a very strong smell and it can interfere with some of the bacteria producing the extra smelly ammonia. However, though there haven’t been any major human studies. So, I wouldn’t advise eating a paradichlorobenzene urinal cake either, no matter how delicious that might sound. Thanks for asking and thanks, especially, to all of our patrons on Patreon who keep these answers coming. If you’d like to submit a question to be answered, or get some videos a few days early, go to and don’t forget to go to youtube.com/scishow and subscribe.

100 thoughts on “Urinal Cakes: Why?

  1. Who kept asking this question that got them to answer it? I mean, I didn't need to watch this video to know that the urinal cakes were obviously for deodorizing the pee in the bathroom, who the hell honestly wouldn't have been able to guess this?

  2. I'm a girl… thought they were talking about someone who crapped in a urinal. XD That's why I watch this show, to get smarter.

  3. Why are urinals there in the first place. If a man SITS on a regular toilet to urinate, that odor won't happen, as the urine will be flushed down the toilet, &, hey, Presto! No odor! Very simple solution–no pun intended.

  4. I'm a year late, but who looks down at a urinal and decides, " That Urinal cake looks delicious."
    Probably a 4 yr old…

  5. This is a bit concerning still. How biodegradable are these chemicals? Are they environmentally toxic like prescription meds after the body has processed & excreted them? We don't like to think about what we flush down the toilet or throw in the trash pretending it dissapears into another dimension rather than hanging around poisoning our enviroment & bodies.

  6. As a woman, this is all new to me! I have no experience with urinals. All you guys take them for granted, but I feel like a spy.

  7. this is relevant for making Storm Glasses. Turns out a lot of stuff sold as Camphor is, in fact, PCB and it doesn't work nearly as well in the reaction.

  8. When your a girl and should not even care about this stuff even tho you kinda always wonder what does the men’s restroom looks like and have ask multiple guys but they are really bad at explaining what it looks like and I had no idea about these things so ya

  9. I used to pick them up with a handful of paper towels and put them by the sink in the men's room. This was years and years ago and I stopped doing it.

  10. Why is the host wearing a flak jacket? 😮 Is he doing this episode in a disputed zone? That's no urinal cake! It's an anti-personnel mine!

  11. Many years ago, I remember these things in certain places and they smelled bad.  I almost would rather smell urine.  They didn't smell like moth balls, so I don't know what they were.  I'm just glad I haven't seen them since in public urinals.

  12. When I was in Highschool there were urinal cakes shaped like honey combs and every time you’d go in the bathroom the ENTIRE bathroom smelled of honey…

  13. The moment I heard Paradichlorobenzen and thought of the song, I finally realized that mayyyybe I have a vocaloid problem

  14. dont use bathrooms with urinals so whenever I heard the phrase “urinal cake” I thought it meant someone pooed in the urinal, I am 18

  15. FUN FACT : When I was in eighth grade my teacher Mr. Bearfield had us melt and then freeze paradichlorobenzene- I think the point was to teach us about freezing and melting points? Anywho, for whatever reason the chemical's name stuck with me. So finally, I have a reason to know this chemical. And I also now know that for the past 2 years I have been using the name of a chemical in urinal cakes to make myself sound smarter. It worked, but damn do I feel stupid right now.

    (I'm also now realizing that my favorite teacher, best I've had, also had the greatest sense of humor. Kudos haha)

  16. It doesn't matter what the cakes are made of… If there's more piss on the floor than in the urinal, nothing is going to help.

  17. As a woman, I had no idea about this and I came here expecting thr plot of that South Park episode where Stan poops on an urinal. I'm lowkey dissapointed.

  18. In my opinion the ‘cakes’ tend to do nothing or very little simply because businesses pretty much forget to replace them

  19. I learned that urinal cakes contain a human carcinogen a few years back and now I always hold my breath when I see one in a bathroom

  20. I was a Supply Sgt. The urinal cakes had warnings that they were hazardous to marine life. They were the only item that had this specific warning.


  22. Paradichlorobenzene!! Yo, anyone else know that song? It’s one of my favorite vocaloid songs of all time. I always wondered what it was!

  23. Omg i saw these in a UK pub, Alwees fresh they were called…lol, and actually the work amazingly. Not sure why these were not invented earlier and used everywhere! Without them the mens bathroom really stinks….

Leave a Reply

Your email address will not be published. Required fields are marked *