Why some fart smells so disgustingly bad, others not so much, and how to avoid them

Almost everyone has missed a fart. The fact is that, farts are not all the same. Some are tremendously sonorous and yet they do not smell. Others are born as spies, tremendously silent, but with noxious smell. What is the reason? Can they be avoided?


Let’s go first with the definition of fart or flatulence. When we talk about them we refer to the mixture of intestinal gases that is expelled by the anus, all accompanied by a sound and, above all, a characteristic smell.

“Ingredients” of a fart

Coming from the intestine, we can have a slight idea of its origin. In fact they can come from three sources: Those produced from food by colonies of intestinal bacteria and symbiotic yeasts living in the gastrointestinal tract, carbon dioxide produced by the neutralization of gastric acid and finally something as simple as air swallowed.

It may seem incredible, but until 1998 science had not identified the exact gases responsible for the smell produced by the fart. It was then that Dr. Michael Levitt used a tube system and rectal pouch to collect “gases” from 16 healthy subjects, 16 volunteers who had eaten an abundant plate of beans the night before.

The study was rather curious, as samples were taken from the bags through a syringe and given to two “expert” judges to determine the intensity. This was correlated with high levels of hydrogen sulphide, methanethiol and dimethyl sulphate.
By the way, Levitt’s work found something disturbing, women’s fart “had a significantly higher concentration of hydrogen sulfide and a greater intensity of smell than men.” Instead, men kept themselves producing more gas in general.

Be that as it may, from the work of the researcher the composition of a human flatulence was extracted, which is composed of:
Nitrogen (70-85%)
Hydrogen (0-50%)
Carbon dioxide (10-30%)
Methane (0-10%)
Oxygen (0-10%)

Today we also know that flatus contains aerosolized particles of excrement, though in minute quantities. Now, the most important part remains. Why the hell do some smell so badly?


Why fart smells worse than others

You probably already knew, but the fart says a lot about our diet. The reason is that the smell depends a lot on what we have eaten. For example, broccoli, onions, eggs and meat contain a lot of sulfur, a chemical that helps give rotten eggs their stench.

When our body digests food, the bacteria in our intestines revel in the proteins of foods that contain sulfur. This process creates foul smelling gases like methanethiol. When those gases leave our body they leave leaving “footprint”.

Also, let’s think that all odors are chemicals in the air that our nose can pick up. As we said, farts are composed of chemicals such as oxygen, nitrogen, hydrogen, methane, carbon and super villain: sulfur. The more sulfur, the more likely it is that the room will smell bad. Finally and as we also pointed out, we also swallow the air while we eat or talk. Some of that comes out of our butt too.


In any case, bacteria are very important in the world of human flatulence. When we eat carbohydrates like potatoes, bread or vegetables, our stomach does not digest them completely. They pass to the small intestine and then to the large intestine, which are really long tubes leading to our anus (where we defecate and expel gases).

Bacteria break down carbohydrates into smaller pieces. This releases gases such as hydrogen and carbon dioxide. Nothing happens, those gases do not smell. However, other bacteria in the gut take these odorless chemicals and turn them into compounds (mixtures of chemicals) that do smell, and much. Hydrogen sulfide is possibly the most disgusting of the gases that could get out of our butt.

In the shower they smell … worse?

Yes, this is true and the reason is very simple. First, because we are trapped in a closed, condensed space. Therefore, farts have no place to emigrate. In addition, unlike when we are out of the shower, we do not have underwear or simply clothes to “block” or absorb part of it.

Having said that, the humidity of the bathroom probably also plays an important role, since water vapor in the air can improve our sense of smell. Scientists do not really know why this happens exactly, but one possibility is that “water vapor helps the molecules that make up the odor and interact with the receptors in the nose” as explained in a video.

Another theory is that gas particles attach to water vapor, as if air were a sponge for frog molecules. This would support more stench than normal dry air.

Can you avoid the smell of “those” farts?

Yes and no. Actually the answer is obvious, if we have some kind of problem or extremely foul-smelling “incontinence” that reproduces too much over time, we should probably change some of the diet.

Most doctors recommend opting for a protein rich if we want to have less flatulence. Some people follow a low-carbohydrate FODMAP diet (FODMAP means fermentable oligosaccharides, disaccharides, monosaccharides and polyols, types of carbohydrates that are not completely absorbed and begin to ferment, causing gas).

Hydrogen sulfide is possibly the most disgusting of the gases that could get out of our butt.
Among the products that are recommended to avoid are apples, pears, watermelons, asparagus, leeks, onions, garlic, avocado, mushrooms and cauliflower. All of them have that diabolical component we were talking about, sulfur.

Finally, products such as rice, corn or potatoes are recommended, in addition to limiting the intake of alcohol and drinking much more water. However, no one escapes that moment forever. Let us hope, for the good of mankind, that science may someday solve the great question: How the hell do we know if a fart will or will not smell before it goes out.


You must log in to post a comment




Password Reset

An email has been set with password reset instructions. If you do not see this email within a few minutes, check your spam folder.

Not Allowed

Your current user level does not allow voting. Please contact the site administrator to upgrade.


Prove your humanity: 2   +   8   =  

Submit A Story

Please login first