This is how you develop a tolerance to tear gas
Corson-Stoughton Gas, commonly known as CS gas or tear gas, is a non-lethal irritant that's often deployed in bouts of civil unrest to disperse riots. The gas "burns" the nose, mouth, and other mucous membranes, causing extreme coughing, partial incapacitation, and a fair share of agony.
Troops typically have to endure a visit to the CS chamber twice throughout their career — first during initial training and once again sometime later. Much like sand, it's coarse, it's rough, it's irritating, and it gets everywhere. Unlike sand, however, it hurts like a motherf*cker.
Oddly enough, the chamber operator or drill sergeant will breathe in the gas like it's nothing because they can handle it. How?
There are some people who are naturally tolerant of CS gas (a suggested 2-5% of the world's population is resistant, with a large percentage of those being of East Asian descent). A mix of both genetics and exposure to an active ingredient in the gas help build a tolerance.
Drill sergeants and CS chamber operators get exposed to the gas on a constant basis over a long period of time. Sure, the first time hurts. The second time, it hurts a little less — and the third time a bit less than that. It's as simple as embracing the suck for long enough.
Even if you're not a drill sergeant with East Asian ancestry, you can still grow a tolerance while at home. The chemical that causes the "burn" is capsaicin. It's the exact same chemical found in chili peppers. This is where the name "pepper spray" comes from.
Now, we're not suggesting that you go home and squirt Sriracha into your face. While there's no official study to back it up, people have claimed that eating a diet full of spicy foods has made their exposures to CS gas and pepper spray milder when compared to the spice-averse.