Many bug repellant are just a mix of artificial fragance/essential oils whose smell repell bugs.
Let’s take the example of lemongrass against mosquitoes. How does-it work ? Does it cancel out the human flesh smell making you invisible for the mosquito ? Or does it smell so bad for the mosquito that they run away ?
I recently found out during a blackout due to a thunderstorm, that candles are a good mosquito repellant.