Citronella is for bugs, lemongrass is for cooking.

They’re different plants, even though they look and smell similar. Both are in the Cymbopogon genus, but citronella is Cymbopogon nardus (or winterianus), and lemongrass is Cymbopogon citratus. The scent is the giveaway: lemongrass is bright, citrusy, and pleasant in food. Citronella is grassier, stronger, and more camphor-like — fine for candle wax, awful in soup.

You can cook with lemongrass. You can’t cook with citronella. It’s bitter and not meant for human consumption. That said, many “citronella” candles actually use lemongrass oil because it’s cheaper. Real citronella works better as a mosquito repellent, but it’s still not great — you’re better off with DEET or picaridin.

Don’t try to make Thai curry with citronella.