When you come home at the end of a long day, you might unwind with a lavender bubble bath.

Or maybe you light a zesty orange candle as part of your study ritual. These habits fall under the umbrella of aromatherapy: the idea that smelling so-called “essential oils” can change your mood or even have healing effects.

It might all sound like pseudoscience, but there have been many studies showing that fragrant essential oils can make you feel more positive, relaxed, or even feel less pain. But, and I’m sure you were waiting for me to say it, it might not only be the oils. There may also be other ways of explaining these effects, too.

Despite their name, essential oils aren’t actually essential at least, not for your body. Instead, they’re found in the bodies of plants, where they’re sometimes used for protection. These oils are complex mixtures of dozens of different compounds that are super small and light.

So unlike other smelly things, they can easily float up and into your nose. Most of these compounds are either terpenes, which are made of chains of carbon and hydrogen atoms, or aromatic compounds, which are carbons and hydrogens arranged in a flat ring. Mixtures of these chemicals will form anything from peppermint oil to lavender oil.

Then, they’re put in candles, lotions, and all sorts of products that can supposedly help you focus or relax. Now, it is worth mentioning that some people claim aromatherapy can treat clinical anxiety, depression, or cancer. But there are few, if any, rigorous studies showing that the oils alone can do those things, no matter what the people selling them advertise.

But, when it comes to relaxation or focus, those effects don’t seem to just be marketing. Tons of studies have shown that all those compounds reaching your nose really can change how you feel. For example, a 2005 study published in the Journal of Physiology and Behaviour looked at how 220 patients waiting in a dentist’s office responded to orange or lavender scents.

The patients either smelled those fragrances wafting around the waiting room, heard some cheerful music, or neither. They were also handed questionnaires to fill in while they waited, which were surveys about things like pain, anxiety, and mood. Those who smelled either orange or lavender said they felt less anxious, more positive, and calmer compared to others who didn’t get the scents or who listened to music.

And there are literally hundreds of other papers showing similar results from other experiments. But even with all those studies, it’s still not clear if the essential oils alone are really responsible for those changes -- or, if they are, how they work. There are some studies in rat brains that suggest essential oils could boost feel-good neurotransmitters in your brain, like dopamine and serotonin.

Or they could dampen the autonomic nervous system, which controls your heart rate and breathing. But why they’d do this isn’t as obvious. As far as we can tell, there’s no specific pathway that’s triggered when these terpenes or aromatic molecules bind to the receptors in your nose.

Instead, it’s more likely that essential oils work for psychological reasons. But, maybe unsurprisingly, figuring out what those reasons are isn’t a walk in the park, either. The research in this field hasn’t exactly been bulletproof, and there are a ton of confounding variables most studies haven’t been designed to account for.

For example, it’s possible that the situation or ritual around inhaling the scent could be more important than the smell itself. One 2006 study showed that new mothers given lavender or citrus oil massages felt less anxious or tired after giving birth. But it may not have just been the smell of the oil.

It could’ve also been that, well, massages are generally soothing. Why these oils work could also just be a matter of preference or even the placebo effect. That’s where the effect comes from your beliefs and not from the properties or chemistry of the treatment.

Or it could be a combination of these things. Right now, the reasons are really hard to pin down because there are some major scientific issues with how many of these studies were done. The biggest, is that few of them are controlled and double blind.

A controlled study compares the test situation to something neutral basically to see if the experimental conditions have any effect. And in a double blind study, neither the participants nor the experimenters know who’s being tested with what. This helps prevent bias.

Another problem is that these studies also often ask people to rate their feelings using a questionnaire. And the questions on these surveys can sometimes skew the results. In that dentist study, for example, patients were asked to rate how calm they felt -- not how they felt in general.

By giving study subjects options for their feelings rather than leaving the question open, that could have made people seem calmer than they actually were. When it comes to scientific evidence, it’s not always about the overall number of studies. If those studies aren’t well-designed, the results won’t be conclusive.

So to really understand how essential oils affect us and why they cause the feelings they do, it would help to have more rigorous research. But while scientists are working on that, all of this doesn’t mean that it’s time to throw out your relaxing bath bombs or perfume diffusers. There is plenty of evidence that using essential oils does something it’s just not clear whether it’s the oils or the experience of using them that’s really responsible for the warm and fuzzy feelings.

Thanks for watching this episode of SciShow! If you liked exploring some of the psychology involved in essential oils, we’ve got the channel for you. You can find even more videos about your mind and how it works over at youtube.com/scishowpsych.