Does Bug Spray Lose Its Effectiveness Over Time?

Important Takeaways

It's always a pleasant surprise when you're lounging on the beach or hiking in a national park and find that the mosquitoes, sand flies, and ticks you anticipated aren't bothering you. However, it's frustrating to spend $20 or more on a full bottle of bug spray, only to discover that it’s no longer effective when you need it most.

Thankfully, the good news is that while bug sprays and insect repellents do eventually expire, it takes a very long time. And if you find an expiration date on the bottle, it usually just means "it may not be as effective."

What Bug Spray Has the Longest Duration of Effectiveness?

How long your bug spray lasts mainly depends on its active ingredients, the substances that keep the bugs away. DEET (N,N-diethyl-meta-toluamide), a common active ingredient in many strong repellents used by hikers and campers in the wilderness, is thought to have an infinite shelf life.

This is because the concentration of DEET doesn't affect the effectiveness of insect repellent; it only determines how long the protection lasts. According to the University of Michigan School of Medicine, a bug spray with 20 percent DEET will provide protection for about five hours, while one with 7 percent DEET will last for two or three hours. That’s why it's a good idea to avoid sunscreen-bug spray combos, as sunscreen needs to be applied much more frequently than bug spray.

Picaridin, a popular alternative to DEET, also boasts an almost infinite shelf life, while IR3535 typically remains effective for about two years before it starts breaking down.

However, many brands like Ranger Ready Repellant and Off! recommend discarding bug spray after three years. On the other hand, Sawyer brand guarantees a 10-year shelf life when properly stored.

Natural bug sprays, which mainly use essential oils as their active ingredients, tend to lose their potency faster than chemical or synthetic alternatives. Common essential oils include rosemary, lemongrass/citronella (two- to three-year shelf life), thyme (three to four years), and peppermint (four to five years). Depending on the concentration of these oils in the spray, effectiveness may begin to decrease after about two years.

A quick, though not always reliable, method to check a natural repellent is to spray some and smell the air. If it no longer has much of a scent, it’s likely not as potent as it used to be. While it won’t harm you, it may not be as effective.

Interestingly, there are no federal regulations requiring food or cosmetics/lotions (except for baby food and formula) to have expiration dates. However, many skin-applied repellents are registered with the Environmental Protection Agency (EPA), meaning the company has submitted technical data to ensure the product’s safety and effectiveness against mosquitoes and/or ticks.

Why Are Expiration Dates Not Included?

If your bug spray does have an expiration date, it's typically voluntary and may be linked to other ingredients like essential oils (which can lose their potency after two years) or benzaldehyde (which has a shelf life of about 18 months and is often found in bee repellents).

Keep in mind that using expired bug spray doesn't carry significant risks, other than its reduced effectiveness, which might leave you with a few more bug bites than you'd like.

If you have a bottle of bug spray you've left unused for a while, the pump and tube might be a bit clogged with dried-up spray, so you'll need to rinse them thoroughly before use. Also, if you're using a cream or rub-on spray, especially one in a clear bottle, store it away from direct sunlight, or it will start to dry out.