Good question! While any pleasant smelling massage helps with mood and relaxation, Aromatherapy mainly works by placebo effect.
If anyone thinks I'm wrong, please provide your robust, peer-reviewed, scientific data showing otherwise.
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EDIT: @a ma tera s, why am I ignorant for requesting data? While you happily offer rubbish advice that didn't answer the question, the best you can offer for evidence to support it is personal attacks on someone who rightly shows skepticism. That makes it pretty obvious that what you are claiming is bogus. Fail.