Fart- A Documentary - Exploring the History of Passing Gas - Only Human

I have researched why dog farts can clear a room.

The Most Relevant Volatile Fatty Acids in Dog Farts:

1. Acetic Acid

Smell: Vinegary

Source: Fermentation of carbohydrates

Volatility: High — easily vaporizes

Contribution to smell: Mild compared to others

2. Propionic Acid

Smell: Slightly pungent, sour, musty

Source: Carbohydrate fermentation

Volatility: Medium-high

Contribution to smell: Noticeable if concentration is high

3. Butyric Acid

Smell: Strongly foul — like rancid butter or vomit

Source: Fermentation of undigested fiber, protein, or fat

Volatility: High

Contribution to smell: Very high — one of the main offenders in stinky farts


While VFAs can make up part of the smelly vapor, the truly offensive part of a fart usually comes from sulfur-containing gases, which are separate from VFAs but often produced alongside them:

Hydrogen sulfide (H₂S) – Rotten egg smell

Methanethiol (CH₃SH) – Rotten cabbage

Dimethyl sulfide ((CH₃)₂S) – Sweet, decaying odor

Ammonia – Pungent, sharp smell (from protein breakdown)

These are not VFAs, but they’re much more potent odor-wise, even in tiny concentrations (parts per billion).

So, Do VFAs Smell Bad?

Yes, some VFAs like butyric acid and propionic acid are volatile and contribute to the odor.

But they aren’t the main cause of that eye-watering stench — that’s mostly due to sulfur compounds.

Summary:

Compound Type Smell Contribution to Fart Odor

Acetic acid VFA Vinegar Mild

Propionic acid VFA Sour/musty Moderate

Butyric acid VFA Rancid butter High

Hydrogen sulfide Sulfur gas Rotten eggs Very High

Methanethiol Sulfur gas Cabbage/sewage Very High

If your dog’s farts are extremely offensive, it’s often because of excess protein fermentation in the colon, which increases both VFAs (especially butyric acid) and sulfur gases.

Would you like help identifying foods that reduce sulfur gas and butyrate production in dogs?

I have seen one dog fart, stop people from being able to breath - they all literally ran from the room. It was so bad. What are the gasses that can cause that, in minute amounts?

What you witnessed — a dog fart so potent it made people flee the room and struggle to breathe — is unfortunately very real and entirely explainable by a handful of incredibly pungent and toxic gases, even when released in microscopic amounts.

Let’s break down the main offenders.

The Most Toxic & Pungent Fart Gases (in minute amounts)

1. Hydrogen Sulfide (H₂S)

Smell: Rotten eggs

Odor threshold: 0.00047 ppm (parts per million) — that’s less than 1 part in 2 million!

Effects:

Eye irritation, sore throat, coughing

Headache, nausea at higher concentrations

Can literally make you gasp or choke in a small, closed room

Source in dogs: Bacterial breakdown of sulfur-containing amino acids (like methionine and cysteine from meat)

The Most Toxic & Pungent Fart Gases (in minute amounts)

1. Hydrogen Sulfide (H₂S)

Smell: Rotten eggs

Odor threshold: 0.00047 ppm (parts per million) — that’s less than 1 part in 2 million!

Effects:

Eye irritation, sore throat, coughing

Headache, nausea at higher concentrations

Can literally make you gasp or choke in a small, closed room

Source in dogs: Bacterial breakdown of sulfur-containing amino acids (like methionine and cysteine from meat)

Additional Gases That Might Be Present (but are less smelly)
Gas Smell Note
Ammonia (NH₃) Sharp, pungent From urea breakdown; more irritating than smelly
Indole Musty, fecal, floral From tryptophan metabolism
Skatole Fecal Same as in literal poop smell
Carbon dioxide Odorless Just a carrier gas
Methane Odorless Highly flammable but doesn’t smell