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 ?
They don’t work that effectively. To the effect they do, they make you smell like poison to mosquitoes.
DEET blocks odorant receptors at a distance and chemoreceptors on contact. Icardin blocks odorant receptors.