It was a long winter for many of us, so the return to warm weather makes upcoming plans for barbecues and picnics sound all the sweeter. Those outdoor activities, of course, come with an itchy, harsh reality: mosquitoes and ticks, as well as the nasty illnesses they spread. How should you protect yourself? Your well-meaning, chemical-fearing friends may push their 100% All-Natural-Chemical-Free-EPA-Approved! insect repellent on you. These balms sound so safe and appealingly natural, and they may have a fresh scent of lemongrass and peppermint. But do they work? Here’s what you need to know.

In the United States, there are two categories of insect repellents: those that are registered and those that are not. The Environmental Protection Agency regulates the distribution, use, and sale of all insect repellents, along with all other pesticides. For registered products, this means that any company that would like to sell a particular pesticide must hand over a slew of safety and efficacy data to the EPA. If the data are sufficient, the EPA registers a label for that product specifying exactly where and how it can be used.

For certain products, there is a loophole—specifically, for those all-natural bug sprays that your well-meaning friend is pressing into your hand at the picnic.

In 1996 the EPA exempted 31 pesticide ingredients from registration, in part to make it easier for companies to bring related products to market. These minimum-risk pesticides, as they’re called, are “demonstrably safe for the intended use” and mainly include foods and essential oils such as citronella, cloves, and mint. Because the EPA has already deemed these ingredients safe, the agency doesn’t need to see related safety data for each new product that includes them. The trouble is, the agency doesn’t require efficacy data either.

Many exempt products boast “EPA-Approved” on their labels, which is a little misleading. For safety, this is true. But this does not mean that the EPA says the products actually work.

(The EPA has a pilot program to potentially change its efficacy requirements for insect repellents in light of West Nile virus and other deadly illnesses. But an EPA representative told me the program has been in place for at least five years and there is “no end in sight.”)

Of course, just because the EPA doesn’t require efficacy data doesn’t mean these ingredients fail to repel biting pests. But the science isn’t promising. Take citronella, among the most commonly sold exempt ingredients. Undiluted, citronella oil may repel mosquitoes for two hours. Common products with 5 percent to 15 percent concentrations, however, may last just 20 to 30 minutes, and other studies suggest citronella candles don’t offer much protection at all. Similar patterns show up for many ingredients on the list, if data even exist. While higher concentrations work best for some of these products, they are also more likely to cause irritation of the eyes, lungs, and skin.

Fixatives such as vanillin, which comes from vanilla bean, and encapsulated formulas, which cradle the ingredients in tiny spheres and release them more slowly, might help specific products last longer, as may mixtures of multiple exempt ingredients. Still, there is too much variation from one product to another to know for sure how well it will work and for how long.

You know what does work? DEET remains one of the most effective and long-lasting insect repellents available. The U.S. Army developed DEET in 1946, and it became commercially available in 1957. That means there is research spanning decades demonstrating that it is safe and effective. Most DEET-fearers, who are wary because it is a chemical (what they actually mean is that it is a synthetic chemical, one not occurring in nature), point to a handful of cases in the 1980s in which children exposed to the repellent suffered seizures. The link between DEET and the seizures remains unclear. The EPA reviewed DEET in 1998 and confirmed its safety, and more recent studies provide further support for its safety. (Of course, it is always important to follow label instructions and to not overuse any chemical, natural or synthetic.)

There are other options that may please everyone. Newer EPA-registered (not just approved) alternatives have proved to be nearly or as effective as DEET. One is picaridin, a synthetic version of piperine, the chemical that gives black pepper its kick; another is IR3535, a biopesticide based on the amino acid alanine that Europeans have used happily for many years and that the EPA approved for use the United States in 1999.

For full-on chemophobes who seek a registered product, there is lemon eucalyptus oil, which works as well as low concentrations of DEET and may last for up to six hours. For adventurous chemophobes, there is PMD, the synthetic version of lemon eucalyptus. Both are generally safe, although neither should be used on children under the age of 3 (just another example of the fact that natural doesn’t always equal benign).

Of course, there are those who will still tout the 100 percent all-natural repellents. They’re welcome to it. I, for one, as a resident of a region plagued with both West Nile virus and Lyme disease, will stick with science and use products with the ingredients recommended to protect against mosquitoes and ticks. Biting, disease-carrying arthropods don’t heed the all-natural fad. I won’t, either.