For someone who constantly deals with gases emitted from strangers' derrieres, Dr. Lester Gottesman sure looks cheery. Then again, how could a man who explains that the signature smell of people's farts is determined at birth not look permanently amused?
In an interview with Vice, Dr. Gottesman covered the big mysteries of gas, such as what determines the signature scent of a fart:
A baby is born with a sterile intestinal track. During the delivery, there's lots of fluid and stool and whatever, and it's thought that at that exposure the baby's colon is populated by the mother's colon bacteria, thereby affecting the smell of the individual's farts for the rest of their lifetime. There's also other theories claiming the colon is populated during the first few months of exposure to fecal material, but that probably doesn't affect the smell as much as the initial intake of feces by the baby during delivery.
He also covered the effect of our favorite beverages have on our bums:
Beer is carbonated, so that's why it makes you fart. Coffee causes the sphincter muscles to relax just a little bit, so you tend to have more farts by accident if you're drinking something with caffeine than if you aren't.
And of course Vice didn't let him go before he explained the phenomenon of oops poops, more crudely known as sharts:
It has to do with the muscles of the anus. There are two muscles of control. One muscle, the internal muscle which is active all the time, it's the one that allows you to sit on that chair without shitting on the chair, then you also have the external muscle which is a voluntary muscle like your biceps. And when you need to hold stool in it will contract, and keep the stool on the inside. The passage that you are describing happens for one of several reasons. One is that the internal muscle has become very labile, meaning any little input inside the anus causes it to relax. Sometimes it relaxes too much, and that can cause stool to slip out. The other reason is you could have hemorrhoids–everybody has hemorrhoids, but people with bigger hemorrhoids sometimes experience gas slipping out between the hemorrhoids and taking with it mucus material produced by the hemorrhoids, which can cause staining of your underwear.