Smelling salts, primarily containing ammonia, can powerfully wake up the brain and body by triggering innate pathways from the nose to the amygdala.

“For instance, the use of smelling salts. I'm not recommending that you do this necessarily, but there are excellent peer-reviewed data showing that indeed if you use smelling salts, which are mostly of the sort um that include ammonia, ammonia is a very toxic scent, but it's toxic in a way that triggers this innate pathway, the pathway from the nose to the amydala and wakes up the brain and body in a major way. This is why they use smelling salts when people pass out. They work because they trigger the fear and kind of overall arousal systems of the brain.”