Summer has returned — and for most of us that means two things for certain: we’ll be outdoors a whole lot more, and we’ll be joined by a variety of biting or otherwise irritating bugs.

Now, more than ever, we need to protect ourselves from insect bites. Flies, mosquitoes, ticks, fleas, chiggers and other blood-sucking critters are becoming much more than just a nuisance. They can transmit serious diseases, ranging from Rocky Mountain spotted fever and chikungunya to malaria, yellow fever, dengue and the Zika virus.

Since it was developed by the U.S. military in the 1940s, a synthetic repellent — N,N-Diethyl-meta-toluamide, or DEET — has served as the primary ingredient for keeping bugs at bay. Some people, however, can’t use DEET at its most effective and longest lasting strength without negative consequences, especially skin rashes, nausea and eye irritation. DEET also can damage certain plastics and synthetic fabrics and it is toxic to various aquatic ecosystems.

Fortunately, there’s an array of reasonably effective alternates, mostly natural oils and plant extracts that are nontoxic. We looked into the science of fending off bugs to review whether, and to what extent, the most popular alternatives to DEET can do the job. Here’s what we found:

Picaridin

Like DEET, picaridin is a synthetic compound formulated to repel insects. It is constituted to resemble the natural compound piperine, which is found in plants producing black pepper.

The EPA reports that it doesn’t have the same neurotoxicity concerns as DEET but still is “slightly toxic” and can cause eye irritation in some users. It is a highly effective repellent and has lasting power of up to 14 hours, about the same as higher concentration formulas of DEET.

There are numerous products available that contain picaridin, with one of the most popular being Sawyer Picaridin Lotion 14-Hour Repellent, available at Cabela’s and other sports and outdoor stores nationwide. Sawyer also markets permethrin, an insecticide that is sprayed on clothing or mosquito nets to kill insects that make contact.

Oil of Lemon Eucalyptus (OLE)

One of the most effective and well-established natural insect repellents comes from the lemon eucalyptus tree (Eucalyptus citriodora). OLE is derived from the distillation of lemon eucalyptus essential oil. Bugs, mosquitoes in particular, hate this sharp-scented oil that can provide protection for up to 12 hours — the best performance among natural repellents.

Repel’s Plant-Based Lemon Eucalyptus Insect Repellent is 30% OLE and has a large following. Some folks, however, find it a bit smelly and greasy.

Citronella Oil

Extracts of pungent citronella derived from lemongrass and combined with essential oils are touted by the EPA as a safe and effective insect repellent. Citronella is particularly effective against Anopheles mosquitoes — the kind that transmit malaria.

Commercial formulas often contain vanillin to reduce evaporation and extend protection for as long as three hours. Concentrations for most products range from 10 to 30% — but because citronella can cause skin sensitivity, many products max out at 10%. Buzz Away makes a handy four-ounce spray bottle.

Neem Oil

This oil is derived from the seeds of the neem tree — a tree indigenous to the Indian subcontinent that is actively cultivated throughout southern and Southeast Asia. By-products of the neem have long been used for their curative properties in Ayurvedic medicine, treating everything from ulcers to acne.

Neem’s efficacy as an insect repellent is not that well-established, however, with only limited study results that show bite-reduction rates of just 25% and protection periods as short as two to three hours. Some recent field studies report better results. A company in the Bahamas called Abaco Neem grows more than 8,000 of its own neem trees and produces a range of repellent products, led by its top-selling Botanical Outdoor Lotion.