Benzoic acid is an organic acid, the conjugate base for sodium benzoate, It’s a good anti-microbial and fungicidal preservative, when it’s in an acidic mixture. It’s not very water soluble, so often you’ll see it used as sodium benzoate, which will dissolve and become benzoic acid. It’s bacteriostatic, which means it limits the growth of bacteria by messing with its metabolism, but doesn’t kill it. It is also a recognized fungicidal ingredient. It works best at pH 5 or lower.