Occasionally, after someone's been, there is an awful acrid smell lying about long after them. What causes this? The food that they've eaten? Urea less dilute due to dehydration?

If it helps I've noticed it only with older males.

  • $\begingroup$ Acrid or like ammonia? $\endgroup$
    – kmm
    Nov 20, 2012 at 22:45
  • $\begingroup$ Acid (not ammonia on the basis that it doesn't smell like cat urine). $\endgroup$
    – Meow
    Nov 20, 2012 at 22:49

3 Answers 3


The odor comes from urea. Urea will slowly undergo displacement to become ammonia, but when it's fresh, it has a strong odor. Other odors do come from food, notably coffee and (in some of the population) asparagus.

  • 1
    $\begingroup$ I always thought that urea was oderless(thus urine not smelling when it is fresh) and that the reaction that urea goes through to be turned into ammonia is what gives that urine smell. $\endgroup$
    – Caters
    Jan 16, 2016 at 22:25
  • $\begingroup$ This answer lacks sources and as far as I understand contradicts two Wikipedia articles 1 2 that state that smell becomes stronger ("worse") with time but is weak in the beginning. Therefore imho this can not answer the awful acrid smell mentioned by OP, unless the toilet was not flushed. $\endgroup$ Jun 28, 2017 at 12:56

Urea could be one. Also, be aware that there are other sources of urine. Asparagus is a famous one. I am still amused because I once thought something was really off with me ( a male, not older yet) when my urine smelled. I panicked and then found out that it was because I had consumed asparagus in a prior meal.

I am not sure if urine starts smelling differently in certain older males, but take diet into consideration.


Urine on the ground smells when there is no rain. Water evaporates, but solutes in it do not. Rain washes solutes deeper into the ground.

In the urine of a healthy person it is urea and bilirubin that smell.

Other causes of smelly urine:

  • Certain foods, like asparagus, onions, garlic and coffee can add to urine odor.
  • Dehydration (more concentrated solutes)
  • Untreated diabetics secrete glucose and ketones in urine
  • Urinary tract infection
  • Liver disease

Here's one source: http://www.healthline.com/health/urine-odor#Diet


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