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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). –  Alyosha Nov 20 '12 at 22:49
    
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3 Answers 3

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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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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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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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