I've heard from "fun fact" sources that there is urine in human saliva:

When you urinate, a small amount of the urine enters your mouth through the saliva glands. But that’s okay – fresh urine is cleaner than saliva.

Other answer sites have short "no" answers, but don't really answer the question.

This article has some information about urea in saliva.

about 12-20mg/100ml.

This article makes no mention of urea, but does say some anaerobic oral bacteria utilize nitrates which would otherwise be expelled in urine.

Our cells do not have much use for nitrate, which is why dietary nitrate floats unused in our blood until we excrete it via urine. [...] Our salivary glands actively accumulate nitrate from the blood and secrete it with the saliva into the mouth.

Are all components of human urine present in human saliva, or only urea and water? Colloquially, is there "pee in spit"?

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    I'm worried this is a "No, by definition" question, rather than an issue of empirical facts. Urine is "a watery, typically yellowish fluid stored in the bladder and discharged through the urethra". Such an answer doesn't seem to address the claim, though. – Oddthinking Nov 4 '15 at 1:43
  • I'm worried you may be right. Thanks for the edit! – Will Nov 4 '15 at 15:07

Not really.

Metaphor: One part doesn't make a whole. Flour isn't a cookie.

According to the European Food Information Council, "The salivary glands in our mouth produce about 1-2 litres of saliva daily. Blood plasma is used as the basis, from which the salivary glands extract some substances and add various others." What are some of those ingredients (according to the Journal of Contemporary Dental Practice):

Salivary fluid is an exocrine secretion consisting of approximately:

  • 99% water
  • A variety of electrolytes (sodium, potassium, calcium, chloride, magnesium, bicarbonate, phosphate) and proteins, represented by enzymes, immunoglobulins and other antimicrobial factors
  • Mucosal glycoproteins
  • Traces of albumin and some polypeptides and oligopeptides of importance to oral health
  • Glucose and nitrogenous products, such as urea and ammonia

Since blood plasma is the catalyst for saliva creation, our other cells do not have much use for nitrate - which is why dietary nitrate floats unused in our blood until we excrete it via urine.

So yes, our saliva contains a component of urine - but one component of urine doesn't make it urine.

Urea vs. Urine

Urea is a nitrogenous waste - but it isn't urine... yet. Urea's molecular formula is CH4N2O. It doesn't have the sulfates and phosphates that urine does.

Urine is nitrogenous waste - but it has much other stuff. Human urine consists primarily of water, with organic solutes including1:

  • urea
  • creatinine
  • uric acid
  • trace amounts of enzymes
  • carbohydrates
  • hormones
  • fatty acids
  • pigments
  • mucins
  • inorganic ions such as sodium (Na+), potassium (K+), chloride (Cl-), magnesium (Mg2+), calcium (Ca2+), ammonium (NH4+), sulfates (SO42-), and phosphates (e.g., PO43-)

Just because we urinate phosphates, nitrates, and sulfates, doesn't mean we are "peeing liquefied mustard gas."

1Composition and Concentrative Properties of Human Urine

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    Please provide some references to support your claims about the contents of urine. – Oddthinking Nov 5 '15 at 3:27
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    @Oddthinking Footnote Added. – Ruut Nov 5 '15 at 5:22
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    This is what I was looking for, now I can respond to this claim with a mustard gas comparison. Thanks! – Will Nov 5 '15 at 23:02
  • I consume blood at every meal: blood has water in it, food I eat has water in it, food = blood. – Nick T Sep 10 '18 at 20:06

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