Eunice Lam 林杏妍

“Flatus” refers to the excess gas in the intestine, and the act of releasing said gas is called “flatulence”, also known conventionally as farting. I know many people laugh immediately when speaking about this topic, but we actually know very little about it, especially the health warnings it may contain. There are many folklores about farts that are not scientifically accurate. Let us break down the myths one by one!

Question 1: “Loud Farts are Not Smelly, Smelly Farts are Silent”(「響屁不臭,臭屁不響」)?

Have you ever farted so loud that your classmates kept laughing at you, so you try to defend yourselves by saying “It wouldn’t be smelly”? Or you are taking a test where you didn’t hear anything but suddenly smell your classmate’s silent “biochemical weapon”? In fact, loudness and odor of the farts are independent of each other.

Loudness is determined by the amount of gases produced. People who fart loudly are probably experiencing indigestion – undigested carbohydrates are fermented by the bacteria in the gut, producing gases such as carbon dioxide and nitrogen. These gases are mostly odorless.

Most of the time, the odor in farts comes mainly from hydrogen sulfide, a gas with rotten egg smell [1]. Individuals who eat more dairy products and meat typically produce more hydrogen sulfide because those foods contain proteins that are rich in sulfur. Interestingly, the hydrogen sulfide produced due to large consumption of sulfur-containing foods is always smaller in volume compared with the carbon dioxide produced by carbohydrate fermentation. Therefore, smelly farts usually build up less gas pressure and are quieter. However, the farts can be both smelly and loud if a person is suffering from indigestion but at the same time consumes too much proteins. Therefore, this saying is not totally correct.

Question 2: Vegetarians Fart More?

In terms of frequency, this is correct. Vegetables and fruits are rich in dietary fiber. Speaking of dietary fiber, there are many kinds apart from cellulose that you may have heard of. Non-digestible oligosaccharides1 are a kind of dietary fiber that humans don’t have enzymes to digest, so they will end up undigested in the large intestine. Interestingly, certain types of bacteria in the large intestine do have the ability to digest these oligosaccharides, and the fermentation process does produce gas, so it is possible that vegetarians generally fart more.

Are vegetarians’ farts smellier then? Apart from meat and dairy products, some vegetables, like cabbage and broccoli, are also rich in sulfur [2]. Since odor depends on the amount of hydrogen sulfide produced, if vegetarians eat a lot of vegetables that are rich in sulfur, their farts could be smelly too. In other words, flatulence from vegetarians and omnivores can be equally smelly!

Question 3: Smelling Farts is Good for Health?

This saying sounds suspiciously like nonsense, but there are some interesting facts that led to the perpetuation of this myth.

As mentioned above, hydrogen sulfide is one of the gases that gives the distinctive smell of farts. Interestingly, extensive research suggested a range of beneficial effects of hydrogen sulfide when it is made within a cell. Hydrogen sulfide can modulate reactions which occur in mitochondria to provide protections to cells under certain conditions, such as high blood glucose caused by diabetes [3]. Mitochondrion is often known as the “powerhouse” of cells because it is the key organelle of energy production in a cell. Mitochondria also play a key role in regulating cell survival. Inspired by the natural protective mechanism, scientists in the University of Exeter have identified a small molecule, AP39, that can direct hydrogen sulfide to the mitochondria of the stressed cells, and release the gas in a very slow manner [3]. This enables us to administer hydrogen sulfide from outside the body and mimic the natural process.

Notably, the scientists remarked at end of their press release that they have never claimed that sniffing hydrogen sulfide can bring any health benefits. This is because for the treatment to be effective, the hydrogen sulfide must be delivered to the right cells at the right dose. Smelling farts is likely not at all effective or beneficial as a form of disease treatment or prevention, because we can neither lead the hydrogen sulfide to the mitochondria of the stressed cells nor control the dose.

Next time when you fart, while having a laugh about it, you should also pay attention to them. If you are constantly farting too much or your farts are abnormally smelly, it may be warning signals from your body that warrant a visit to the doctor’s office.

Oligosaccharide: A saccharide polymer that consists of 3-10 monosaccharides as monomers


[1] Xu, B., Xu, H., & Liang, J. (2009). Wei Chang Jue Ding Ni De Jian Kang [Your Digestive System Affects Your Health]. Taiwan: Business Weekly Publications, Inc.

[2] Dove, L. L. (2015, June 04). Do vegetarians have smellier farts? Retrieved December 27, 2018, from

[3] Guo, W., Kan, J., Cheng, Z., Chen, J., Shen, Y., Xu, J., . . . Zhu, Y. (2012). Hydrogen Sulfide as an Endogenous Modulator in Mitochondria and Mitochondria Dysfunction. Oxidative Medicine and Cellular Longevity, 2012.

[4] University of Exeter. (2014, July 9). Retrieved December 28, 2018, from