Essential oils have been in use for nearly 6,000 years — intended for therapeutic, hygienic and spiritual purposes — and they remain quite popular today. Claims about their benefits range from stress and pain relief to insomnia and psoriasis treatment, with a global market expected to reach $14.1 billion by 2026.  But each vial of extract has a limited shelf life that consumers should consider. Can Essential Oils go Bad? Essential oils are concentrated extracts made from steaming or pressing the roots, leaves, seeds or blossoms of various plants. Producing a single bottle of essential oil may require large quantities of a single plant.  “Everything natural degrades — food, wine, plant extracts, vegetable oils and essential oils,” says Robert Tisserand, aromatherapy expert and founder of Tisserand Institute, an online education portal for the safe use of essential oils. Like fruit, essential oils oxidize, which means the components of the oil change chemically when exposed to oxygen, he adds.  In addition to oxygen, exposure to light, heat, moisture and microorganisms can also cause oils to break down and go bad, says Elisabeth Anderson, director of science communication at the Center for Research on Ingredient Safety at Michigan State University. How Long Do Essential Oils Last? On average, essential oils can last about two years when stored appropriately. However, they possess unique properties and components that affect their lifespan, so it generally varies between different oils and manufacturers, says Anderson. Since the shelf life can be anywhere from one year to several years, Tisserand suggests “starting the clock” from the time the essential oil is purchased. “The ones that degrade the quickest are ‘light’ essential oils like citrus, conifer, eucalyptus and frankincense oils, [about] one to two years,” says Tisserand. “These oils are composed of the smallest molecules. The ones that last the longest are ‘heavy’ oils like sandalwood, patchouli and vetiver, about five years.” Most other oils last around two to three years, he adds. Recognize the Signs of Expiration Tisserand says it’s not always easy to tell when a bottle of oil has expired because it happens gradually. Like with most products, you need to use your senses to determine if the essential oil has gone bad, says Anderson. “If an essential oil changes viscosity, develops an undesirable smell, looks murky or cloudy, or changes state in any undesirable way, you should not use it,” she adds. Read More: Is ‘Expired’ Milk Safe to Drink? Here’s How to Know When to Throw Away Food Using expired essential oils is not advisable because it may lead to adverse outcomes. “If the oil has gone rancid due to oxidation, it may simply smell bad,” says Anderson. “However, if it’s gone bad due to a microorganism, it could cause harm if it gets into a wound.” To look into the safety of essential oils and botanicals even further, the National Institute of Environmental Health Sciences joined forces with the U.S. Food and Drug Administration and the nonprofit Health and Environmental Sciences Institute to establish the Botanical Safety Consortium. Research about the potential health effects of short- and long-term exposure to botanicals, including essential oils, is underway. Read More: Essential Oils Could Impact Your Memory and Reaction Times How to Store Essential Oils Knowing how to store essential oils is a must to protect their composition and keep them from going bad. For instance, refrain from leaving bottles inside a car. Heat encourages oxidation, says Tisserand. It’s best to keep essential oils in cool, dry, temperature-controlled areas out of direct sunlight, says Anderson. Storing essential oils in bottles that can filter out ultraviolet (UV) light will also maintain their lifespan, she adds. “Essential oils should always be in amber glass bottles,” says Tisserand. “Blue glass is not quite as good, and green glass is even less useful.” Preserving Essential Oils Amber glass provides UV light protection, that’s why it’s preferred for light-sensitive products like essential oils, pharmaceuticals and certain food and beauty products. Make sure you keep the lid on tight, not just to avoid spillage, but also to reduce its exposure to air. “When you open a bottle, don’t leave the cap off longer than you need to,” says Tisserand. “The more air that is in the bottle, the quicker the oil will oxidize.” You may keep essential oils in a small, dedicated refrigerator to help preserve the oil, says Tisserand. And if they’re in the fridge, you don’t need to be concerned about exposure to sunlight, he adds. “Additionally, not touching the oils directly with your hands can help keep out microorganisms that can further accelerate deterioration,” says Anderson. Overall, anyone can maximize the lifespan of essential oils as long as they are used and stored properly. Read More: What Science Says About the Potential Healing Effects of Essential Oils