Why does pre-defecation flatulance smell so much worse than post-defecation flatulence?

Pre-defecation flatulence, or farting before you go to the toilet, may smell worse than post-defecation flatulance because of the food we eat and how it is digested.

There are two types of gas that form part of human flatulence: volatile sulfur compounds (VSCs) and odorless gases such as carbon dioxide and hydrogen. VSCs are produced from the breakdown of proteins into amino acids in our gut, producing a sulfurous odor.

The foods we eat contain different combinations and quantities of protein which explain why sometimes people fart more smelly farts than other times. For example, red meat contains high levels of a protein called cysteine which produces especially smelly VSCs when broken down in the gut. Eating too much garlic or onions also can cause a very pungent smelling gas due to their sulfur content breaking down during digestion. On top of this certain bacteria in our digestive system also produce additional foul smelling gases when they ferment sugars found in some foods such as beans, lentils etc..

As well as what type and amount we’re eating; how fast it passes through us affects both its look/texture (poop) and smell (fart). If digestion happens quickly then there is less time for those smelly VSCs to become created so resulting pre-defecation flatulance will smell less compared to if food had been present longer in our intestines giving bacteria more opportunity to break down complex proteins into stinky molecular components! Therefore depending on what you ate recently; pre-defecation farts can be significantly worse smelling than post defecation ones!