A polite chemical bouncer that convinces mosquitoes you're simply not their type tonight.
means A substance that drives something away — typically insects — or, as an adjective, something so off-putting it makes you instinctively recoil.
from From Latin repellere, 'to drive back,' built from re- ('back') and pellere ('to push, to drive'). That same pellere muscle flexes through a whole family of pushy English words — compel, expel, propel, dispel — all of them shoving in slightly different directions. A repellent simply pushes back, whether it's keeping mosquitoes at bay or describing a person you'd very much like to keep at one.
deet — chemical compound developed by us army in 1946, found in most commercial insect repellents
picaridin — synthetic repellent created by bayer in 1998, now in sawyer and natrapel products
permethrin — insecticide used on clothing and gear since 1970s, kills insects on contact rather than repelling