Farts smell mainly because of tiny amounts of sulfur-containing gases made by gut bacteria as they break down food, especially certain fibers and proteins.

What actually makes the smell

  • Most of the gas you pass (nitrogen, hydrogen, carbon dioxide, methane) is odorless.
  • The stink comes from sulfur compounds produced by gut bacteria, mainly:
    • Hydrogen sulfide (classic “rotten egg” smell).
* Methanethiol (like rotting vegetables or garlic).

* Dimethyl sulfide (cabbage-like, sometimes slightly sweet).
  • These sulfur gases are less than about 1% of the total gas volume, but they’re extremely potent to the nose.

What foods make farts smell

Certain foods give bacteria more sulfur or more fermentable material to work with, so the gas smells stronger.

  • Sulfur-rich veggies:
    • Broccoli, cabbage, cauliflower, Brussels sprouts, onions, garlic.
  • High-protein foods:
    • Beef, chicken, eggs, some processed meats.
  • High-fiber / high-FODMAP foods:
    • Beans, lentils, some whole grains, and certain fruits make more gas in general, which can carry more odor.

When smelly gas is still normal

  • Passing gas 13–21 times a day is considered normal, and many of those farts won’t smell much at all.
  • Brief episodes of really bad-smelling farts often link to:
    • A recent heavy meal, especially rich, garlicky, or cruciferous foods.
* Mild constipation, which leaves food in the colon longer so bacteria can make more smelly byproducts.

When smell might signal a problem

Occasionally, very foul gas plus other symptoms can be a clue about the gut.

  • Possible contributors:
    • Food intolerances (like lactose intolerance) or difficulty digesting certain carbs.
* Conditions such as irritable bowel syndrome or celiac disease, which can change how food is broken down and fermented.
  • It’s smart to talk to a doctor if smelly gas comes with:
    • Persistent diarrhea or constipation, weight loss, blood in stool, or new, ongoing belly pain.

Fun “quick scoop” angle

  • Most farts don’t smell; it’s the rare, sulfur-packed 1% that clears the room.
  • Online forums and joke communities love playing with this topic, often joking that farts “smell so deaf people can enjoy them too,” showing how common and light-hearted the discussion is.

TL;DR: The answer to “what makes farts smell” is: sulfur gases from gut bacteria digesting certain foods, especially sulfur-heavy veggies and proteins; the rest of the gas is basically odorless.

Information gathered from public forums or data available on the internet and portrayed here.