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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.

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Acrid or like ammonia? – kmm Nov 20 '12 at 22:45
Acid (not ammonia on the basis that it doesn't smell like cat urine). – Meow Nov 20 '12 at 22:49
If you have received an acceptable answer, please be so courteous and select the appropriate checkmark. – user560 Nov 26 '12 at 16:23
up vote 3 down vote accepted

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.

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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. – Caters Jan 16 at 22:25

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.

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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:

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