The weather is warming up, which means mosquitoes and ticks will start biting soon. Some spread nasty illnesses, from West Nile Virus to Lyme Disease. With a preference for natural products on the rise, YouBeauty asks: Do botanical bug sprays really protect you, or should you reach for the DEET?Insect repellents in the U.S. fall into two broad categories: registered and unregistered. Registered means that the companies that make the repellents have submitted data to the Environmental Protection Agency (EPA) showing the ingredients are safe and that they work, and the EPA has agreed and allowed the product to go to market.Registered repellents include synthetics, such as DEET and Picaridin, as well as a few derived from natural ingredients, including lemon eucalyptus oil, PMD and IR3535. The Centers for Disease Control recommend products with these ingredients for protection against biting, disease-spreading mosquitoes, and health experts in Connecticut, the state where Lyme Disease was discovered, recommend some to ward off ticks. To figure out if a specific product is registered, look for an EPA registration number on the label.Unregistered ingredients fall under section 25(b) of the Federal Insecticide, Fungicide, and Rodenticide Act, which is what gives the EPA the power to regulate pesticides, including repellents. There are 31 active ingredients on the list, and these are exempt from registration because they are generally considered safe. But, because they aren’t registered, they are also not officially tested for efficacy, which means there may be scant evidence that they actually work. Most are essential oils or common food ingredients.Sometimes, unregistered products will include language like, “100% natural oils approved by the EPA.” This just means the EPA considers these oils safe for use; it does not mean the agency says they will work against bugs.If a product lists an active ingredient in a repellent that is not EPA-registered or is not on the 25(b) list, then it isn’t a legal pesticide in the U.S.Here is the breakdown on some of the most common active repellent ingredients and whether there is science backing up their claims:Name: DEET (N, N-diethyl-meta-toluamide)What it is: A synthetic repellent. The U.S. Army developed DEET in 1946, and it’s been registered for commercial use since 1957.Does it work? DEET is EPA-registered, which means the agency has seen data that shows the ingredient works. DEET is widely considered the most effective insect repellent and lasts longer than most alternatives. According to the EPA’s list of registered DEET products, the repellent lasts between two and 12 hours, depending on the formulation and concentration.Is it safe? Yes, if used according to directions on the label. Both the EPA and the CDC cite reports associating DEET with seizures, but there is no firm data linking the two.Name: PicaridinWhat it is: A synthetic version of piperine, the main chemical in black pepper.Does it work? Picaridin is EPA-registered, so there is strong data that shows that it works, and the CDC rate it among the most effective repellents. Concentration and formulation impacts how well it works and for how long. See the EPA’s list for specific products, which can last anywhere from three to 14 hours.Is it safe? Yes, if used according to directions on the label.Name: Lemon eucalyptus oil/ PMD (p-Menthane-3,8-diol)What it is: Lemon eucalyptus is a common name for Corymbia citriodora, a tree that grows in eastern Australia (other common names: lemon-scented gum or a spotted gum). PMD is a synthetic version of lemon eucalyptus.Does it work? Both versions are EPA-registered, so there is strong data that indicates that they work. In fact, some data suggest both are just as good as low levels of DEET, although it always will depend on concentration and formulation. See the EPA’s list for specific products for lemon eucalyptus and for PMD, which last about six and two hours, respectively.Is it safe? Yes, if used according to directions on the label. Both products are not, however, considered safe for children under three.Name: IR3535What it is: Although IR3535 is synthetic, the EPA classifies it as a biopesticide because it is derived from natural ingredients, specifically alanine, an amino acid. Its chemical name is 3-[N-Butyl-N-acetyl]-aminopropionic acid, ethyl ester.Does it work? Since it is a registered product, there is data supporting its efficacy. Concentrations and formulations will impact results. See the EPA’s list for specific products, which last between two and 10 hours.Is it safe? Yes, if used according to directions on the label.Name: Citronella oilWhat it is: This oil is distilled from Cymbopogon grasses. There are two main commercial variants: Ceylon type and Java type.Does it work? In some cases, cintronella works against certain mosquito species, but not for very long. A 2005 study showed that undiluted citronella protected against two species for two hours. But, most products use diluted oils, and the results from these vary. A 2008 study said common products with 5 percent to 15 percent concentrations only lasted between 20 and 30 minutes, while a 2011 study found that a 10 percent formulation combined with soybean oil, another 25(b) ingredient, lasted between 48 and 88 minutes, depending on the mosquito species. A 2013 study found citronella candles ineffective against mosquitoes.Is it safe? Yes, although the EPA notes that it may irritate the eyes and skin. Generally, though, it is considered safe and is a 25(b) ingredient.Name: LemongrassWhat it is: Like citronella, lemongrass oil is distilled from Cymbopogon grasses, although it comes from different species.Does it work? Also like citronella, lemongrass shows some repellency against mosquitoes, but it typically lasts a couple of hours or less.Is it safe? Lemongrass is a 25(b) ingredient, so it is considered safe by the EPA. Since it’s closely related to citronella, lemongrass can also irritate eyes and skin.Name: Cedar oilWhat it is: This oil is typically distilled from the wood of cedar, juniper or cypress trees. It is sometimes also called cedarwood oil.Does it work? There is very little peer-reviewed research that examines cedar oil as a repellent and no clear consensus on whether it works. A 1999 study found one type of the oil didn’t work against two mosquito species, while a 1984 study claimed some effectiveness against a different species. In 2012, the Federal Trade Commission brought action against a company peddling a cedar-based product to treat bed bug infestations (it also claimed it worked against head lice). The company apparently did not have sufficient data to back up its marketing claims.Is it safe? Yes, for short-term use, although studies on mice and on people who work in saw mills show extensive exposure may be toxic to both the liver and the lungs. The EPA lists cedar oil as a 25(b) ingredient, it falls under the FDA’s Generally Recognized as Safe category, and it is also a common ingredient in lotions and other cosmetics.Name: Clove oilWhat it is: Oil distilled from the clove plant, Syzygium aromaticum. Its main component is eugenol.Does it work? The science is mixed. A 1999 study said it was ineffective against mosquitoes at 5 to 10 percent concentrations, although at higher concentrations it worked for up to three and a half hours. A 2005 study showed clove was mostly ineffective against mosquitoes at up to 50 percent concentrations, while 100 percent concentrations provided two to four hours of relief (most products, of course, have much lower concentrations).Is it safe? The EPA lists clove oil as a 25(b) ingredient and it falls under the FDA’s Generally Recognized as Safe category, but high concentrations might irritate the skin.MORE: Bugging Out? Nine Natural Insect Repellents No matter which repellent you choose, always remember to follow the instructions on the label: These are the conditions under which the product and its active ingredients have been tested and deemed safe. Research on unregistered botanical ingredients suggests wildly different protection times, but overall these typically don’t last very long, so reapply according to the label. Formulations that have multiple ingredients or that mention encapsulated oils or vanillin, a fixative sourced from vanilla bean, may increase a product’s staying power, but there’s no concrete evidence.But, if you live in an area with high levels of West Nile, Lyme Disease or any other pest-spread illness, it is safest to use stronger synthetics such as DEET or picaridin or a registered botanical such as lemon eucalyptus, as recommended by the CDC or other health organizations.