Citronella oil is an essential oil that's made from the distillation of the Asian grass plant in the Cymbopogon genus. This fragrant grass got its name from the French word meaning lemon balm, due to its floral, citrus-like aroma. Oil of citronella is a naturally occurring insect and animal repellent distilled from two grass varieties. It is yellow to brown and has a grassy/floral smell.