Is that leftover bug spray from last summer still effective? This is when it expires

mother spraying insect repellent on child’s arms outdoors

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The arrival of warmer weather brings many exciting things, including longer days, backyard barbecues and beach trips. One thing that we can almost assure you no one is looking forward to when the temperatures start to rise is insects. Pesky critters do everything from bite and sting to swarm around your food. That’s why it’s useful to have some kind of insect repellent on hand to ward off mosquitoes, flies, and other unwanted insects. If you still have a lost bottle or two in your medicine cabinet, you might be wondering: do insect repellents expire? If so, how long does it last? To help you answer these questions, we consulted a few experts.

The most common active ingredients in insect repellents are DEET, picaridin, IR3535, and lemon eucalyptus oil, all of which are approved by the Centers for Disease Control and Prevention. Although these additives are quite stable and can last a long time, it is recommended that the insect repellent be discarded after three years. This is not necessarily because the product expires, but rather because it loses its effectiveness. “Expiration dates are not required on packages unless the product expires in less than three years,” says Laura Patel, director of marketing at Murphy’s Naturals. She notes that most repellents include a lot code on their packaging, which consumers can use to find out more about a specific product.

Related: 11 Natural Mosquito Repellents to Keep Bugs Away This Summer

Many all-natural insect repellents use lemon eucalyptus oil as the active ingredient. Patel explains that this CDC-approved additive never goes bad, but it can become less effective over time. “If the product doesn’t smell as strong as it normally does, or if the product looks damaged, it may be expired,” she says. In general, it’s best to be careful with oil-based repellents, notes Nichole Powell, founder and CEO of Kinfield, which creates all-natural products for the outdoors, including repellents. “Essential oils don’t spoil like a food might, but they do change over time in unpredictable ways,” she explains. If you notice any changes in odor, texture, or appearance, Powell recommends discarding the product.

However, not all insect repellents use essential oils as the active ingredient. DEET, a chemical found in many popular brands of insect repellents, is an effective and highly stable ingredient that, like oil-based products, has no expiration date. It’s important to note, however, that even DEET-based formulas can lose their punch over time. “Expiration dates vary by ingredient and production date, so it’s important to check with the manufacturer to make sure your product is still effective and safe to use,” says Patel.

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