We'll take lavender oil: it's molecular shape of real lavender essential oils fits into the stress receptors of the brain, blocking the brain from receiving stress signals, calming you down.

The molecular shape of synthetic lavender oil doesn't even come close, but that doesn't mean it doesn't always work. If you use the real essential oil enough, it will train your brain to associate the scent with calm and kind of do it on its own. (Pavlonian responce).

HOWEVER what that synthetic oil does do is a dependent on what they use to make that scent. It may send your brain into inflammation mode or irritate your sinuses, etc. It's why some people can't go into candle shops.

Ultimately it's far better to check the ingredients.

Just a bit of how essential oils works.

I grabbed a quick address for citation.

https://www.takingcharge.csh.umn.edu/how-do-essential-oils-work#:~:text=During inhalation, odor molecules travel,as the "emotional brain."