Among the crunchy set, essential oils have a reputation as catch-all solutions to major health problems. Have a fever? Rub peppermint oil on your feet. Suffering from shoddy memory? Put some rosemary oil in a diffuser. It doesn’t help that woo-woo bloggers are running around the internet touting the glory of essential oils in the same breath as some pretty paranoid fantasies (“This is what Big Pharma doesn’t want you to know!!!111”).

So, what’s the truth behind essential oils? Do they help? Do they harm? Are they just useless placebos? Are there real health benefits? We dug into the research and spoke to experts in the field to figure out what essential oils are, how they work, and what they really can do for you.

So what are essential oils?

Essential oils are also known as volatile oils because they evaporate quickly after coming in contact with oxygen. An essential oil is, simply put, the “essence” of a plant, obtained by water or steam distillation, or by cold pressing (for citrus peel oils). Through this process, the oils inside a plant can be extracted into a highly concentrated form.

“When you smell an essential oil,” says Tony Ferrari, Ph.D. in chemistry, “its constituents bind to receptor sites in the nose, which read the aroma molecules and send signals through the olfactory nerve to the limbic system and amygdala in the brain. There are more than 5,000 chemical compounds that make up commonly used oils, each of which binds in a different way to different receptors, so their effects can vary widely.”

How do essential oils work?

“Essential oils include biological compounds like growth factors, hormones, and neurotransmitters that are concentrated from the plant,” says Nada Milo, M.D. “Because different essential oils come from different plants, these components (and their resulting effectiveness) tend to change from plant to plant.”

Essential oils can have complex biochemical interactions in the human body, she says—and different essential oils can create different reactions in our enzymes and hormones. One of the active ingredients in tea tree oil, for example, is Terpinen-4-ol, which was shown in studies to kill ectoparasites found on human skin and kill infectious amoebas that cause eye infections.

One unpleasant—but totally effective—parallel you’d find in nature is poison ivy: We react to poison ivy with those awful, itchy-as-all-get-out red bumps because we’re exposed to an active compound in the plant that interacts with our skin. Elizabeth Trattner, M.D., explains that essential oils work differently—but they’re even stronger. “Essential oils can be up to 100 times more potent than the plant itself,” she says. “So their effects are visible with just a few drops.”

Basically, the active ingredients inside an essential oil can trigger “switches” inside our body. “Here’s another example,” Milo says. “An EO like lavender can stimulate olfactory nerves in the brain and cause downstream effects that slow down the central nervous system and induce a sense of calm.”

So not all essential oils are going to work as advertised. They’re derived from a variety of plants, all of which have different effects on the body (and some of which aren’t that effective). On top of that, you have to consider the method of application—are you rubbing it onto your skin, ingesting it in a capsule, or simply sniffing it?

Be careful—some methods of applying essential oils are safer than others.

“Untrained lay people, especially in the multilevel marketing (MLM) business, will say anything to make a sale,” Trattner explains. Some folks, especially MLM bloggers—and even some big companies—suggest methods for essential oil use, without informing people of the dangers of using essential oils incorrectly. They’ll say that you can use them anytime, anywhere. In demonstrations, they might dab some on their wrist or talk about how oils can be used in capsules.

This is something to be wary of, says David Lortscher, M.D. “People have to be careful about how they use these products. Essential oils have the potential to sensitize and irritate skin. There have been rare reports of serious toxicities, including seizures, adverse effects in pregnancy, and lung or liver toxicity.”

For example, linalool, the main component of lavender essential oil, has been shown in studies to cause skin cell death and increase the risks of contact dermatitis. “In general, though,” he continues, “these EOs are pretty safe. When irritation does happen, it’s usually mild and limited to the skin.”

To minimize the risks of topical essential oil application, it’s best to dilute essential oils with a carrier oil, or a neutral oil that can contain the essential oil. “Most allergic reactions are caused by the application of pure oils, or high-concentration products,” Lortscher says. “But if you tolerate them or dilute them, they can help with dry, flaky skin, provide some antioxidant benefits, and also help relax your body.”

Many essential oils companies sell their EOs undiluted, so you’ll have to dilute them yourself (NAHA provides some guidelines on safe dilution). Adults should dilute an essential oil anywhere from 2.5 to 10 percent; for a 10 percent dilution, for example, you’d use 60 drops of essential oil per ounce of carrier. Some of the most common carrier oils are jojoba, coconut, and sesame oil.

What about the claims that essential oils are perfectly safe to ingest? That’s not necessarily true. Essential oils are broken down in the liver into phytochemicals, and if they accumulate, they can become toxic to the body. While a study of one is hardly convincing evidence, a woman who ingested peppermint oil was brought to the hospital in a comatose state.

“Oral ingestion results in ten times the amount of absorption into the bloodstream of an essential oil compared to topical application,” Ferrari says. “This type of application is usually used for short-term treatment of more serious ailments, like bacterial infections (some essential oils are effective against the MRSA bacteria, for example), viral infections, and even cancer.”

Cancer? Really? “Yes,” Ferrari says. “Though this isn’t widely accepted by the medical community, there are actually quite a few studies showing that essential oils can cause cancerous cell lines to die via apoptosis.” But lots—and lots—more research needs to be done before this kind of treatment can be considered viable.

In any case, Ferrari says, it’s important to tread carefully around oral consumption of essential oils. The National Association for Holistic Aromatherapy offers several warnings against oral consumption of certain essential oils (“they may cause heartburn, nausea, and vomiting,” which, no thanks).

For example, peppermint is one you may want to avoid. Clove oil is another one you should probably stay away from (in one case, it caused a coma and acute liver damage). NAHA notes that people shouldn’t take essential oils internally without appropriate education and an understanding of the resulting safety issues.

Basically, our take is that ingestion should be medically prescribed and regulated by a doctor who has experience with essential oils—you definitely shouldn’t try and make your own capsules at home.

So how can essential oils be used safely—and which EOs have actual health benefits?

Essential oils have been used in aromatherapy for hundreds of years. Our sense of smell (controlled by the olfactory nerve) is very powerful and exerts influence over our thoughts, emotions, moods, memories, and behaviors.

“Essential oils can reduce inflammation or stimulate the immune system or calm down the autonomic nervous system,” Ferrari says.

If you’re feeling confused, stick with the basics. “Lavender oil is a great EO for beginners. You can inhale it before sleeping, pour a few drops into a diffuser, or rub it onto your pressure points (neck, wrists, and other places where your pulse is most prominent). Plenty of studies have been done on lavender oil to demonstrate its efficacy,” Trattner says.

One such study demonstrated that inhaling lavender oil increased the power of alpha and theta brain activities, resulting in significant decreases in blood pressure, heart rate, and skin temperature. Granted, this was from a sample size of 20, so—take the results with a grain of salt.

But another, slightly larger study supported these results and showed that the same method of application (inhalation) before bed significantly decreased anxiety levels and greatly improved sleep quality in patients. Inhaling lavender oil for 30 minutes a day during your period can also reduce the severity of menstrual cramps.

If you’d like to use essential oils for digestive problems, you can ask your doctor about rosemary capsules, which have been demonstrated in studies to inhibit E. coli overgrowth and effectively treat ulcers. The ingredients at work inside rosemary oil are caffeic acid, and its derivative, rosmarinic acid, which have antioxidant effects.

Bergamot, another essential oil with “multitasking” capabilities, is often used as part of a treatment for depression because of its ability to reduce stress responses. When inserted into oil diffusers, it helped create a positive mood in patients. Besides its uplifting effect on mood, it can also be used as an antibacterial and antifungal agent against E. coli, Listeria monocytogenes, Staphylococcus aureus, and Bacillus cereus.

Does quality matter?

You’ll often see companies advertising their “therapeutic grade,” “aromatherapy grade,” or “medicinal grade” oils. Unfortunately for them, no such thing exists. “There is no formally approved grading standard used consistently throughout the essential oil industry,” Lortscher says. Simply put, anyone who says that they have therapeutic grade or “certified” essential oils is lying. “That seal is nothing more than a commercial trademark. It isn’t backed by any scientific body.”

So how can we tell whether our essential oils are pure or not? Is the market even regulated?

“The only rules in place in the EO market are those set by the ISO (International Organization for Standardization), which states that essential oils must be natural and pure,” Lortscher says. “A pure essential oil is very volatile, so it should not leave any residue on a white blotting paper. It also shouldn’t smell rancid or like alcohol.”

“Don’t be cheap about essential oils,” he says. “Cheap essential oils are almost guaranteed to have synthetic oils or mineral oils mixed inside. Another thing to look out for is the country of origin—oils sourced from plants native or indigenous to their regions are far more trustworthy.

What about synthetic oils?

“Synthetic essential oils may seem like a bargain,” says Rupinder Mangat, CEO of Mevei. “It can be difficult to tell the difference between a synthetic oil or a real one. But be careful—chemically reconstructed oils seldom include all the trace chemicals that are found in the real plant. Price can be an indication that an oil is synthetically reproduced or extended.”

How can you ensure that your essential oils are pure?

Lortscher says that the purity of different EO’s can vary widely, based on the degree of concentration and where they’re sourced from. “On top of that, the quality of your oils can be affected by adulteration (the purposeful addition of foreign substances), unintentional contamination, inadequate production, or improper storage conditions,” he says. “If you keep an essential oil exposed to bright sunlight or oxygen, the composition of the oil can change. It’s best to store them in a cool, dark place.”

To make sure that your essential oils are pure, you can ask the company if they do mass spectrometry testing. These tests check to see how pure an essential oil is and can be used to see if the oil has been altered or added to.

The final verdict?

When used in aromatherapy or if diluted for topical use, essential oils can be safe—and helpful. While no essential oil is going to cure asthma or banish migraines, they can help with a variety of health issues.

“Essential oils like lavender and rose can be excellent adjunctive therapy to many health issues like inflammation, pain, and high stress or anxiety levels,” Trattner says. “And they can be used as the first line of defense to prevent conditions from developing or worsening. Do I recommend them to my patients? All the time—and I’ve been practicing for over two decades. But they aren’t one-size-fits-all, and they aren’t magic potions, either. If there’s too much pain or you’re facing a severe disease, then it’s time to take something stronger or talk to your doctor to create a cohesive plan of action.”

Basically, use essential oils with caution and do your research on the specific oils you plan on using. If you have any questions or doubts, make sure to ask your doctor. Used correctly, essential oils can greatly enhance your life—just don’t expect major miracles out of them.

Theodora Sarah Abigail is a beating heart in a warm body. She works as a writer and poet in the wild, mechanical city of Jakarta, Indonesia. You can join her as she stumbles through life by following her on her blog and on Instagram.