Yes and no. It depends on the concentration. Here’s the important thing to understand: Essentially all insect repellents effectively keep mosquitoes at bay. They just vary in how long they work before they must be reapplied. And therein lies the rub.

Oil of lemon eucalyptus is a naturally occurring chemical, unlike DEET and picaridin, which are synthetic man-made substances. Refined from the oil produced by a specific variety of eucalyptus tree (Corymbia citriodora), oil of lemon eucalyptus can also be produced synthetically and is then referred to by its chemical name p-Menthane-3,8-diol, or PMD. In commercial products, it is usually referred to as oil of lemon eucalyptus, or by its trade name, Citriodiol.

If you’re really interested, you can dig into its chemistry and origins on Wikipedia, or in this excellent 2011 overview of plant-based repellents in Malaria Journal.

Oil of lemon eucalyptus is generally considered to be the most effective natural repellent on the market. In 2005, the Centers for Disease Control added PMD to its list of recommended insect repellents, based on evidence from recent studies that found repellents with concentrations of 30 percent PMD generally provide about two hours of full protection from mosquitoes and up to six hours under certain conditions, which is roughly equivalent to repellents with 10 to 15 percent DEET. However, it provides significantly less duration of protection than higher concentrations (20 to 50 percent) of DEET and picaridin, which completely repel mosquitoes for five hours or more.

If, however, you are concerned about the caustic nature of DEET and its ability to dissolve plastic, or wary of using a relatively new synthetic chemical like picaridin, than oil of lemon eucalyptus is probably a good bet for you. But beware—the stuff has a cloying and extremely pungent odor that can start to permeate anything stored with it. I strongly recommend sealing it tight (and double-bagging it) in zip-locks bag when not in use.