Some benefits that have been linked to aromatherapy, such as relaxation and clarity of mind, may arise from the placebo effect rather than from any actual physiological effect. The consensus among most medical professionals is that while some aromas have demonstrated effects on mood and relaxation and may have related benefits for patients, there is currently insufficient evidence to support the claims made for aromatherapy. Scientific research on the cause and effects of aromatherapy is limited, although in vitro testing has revealed some antibacterial and antiviral effects. There is no evidence of any long-term results from an aromatherapy massage other than the pleasure achieved from a pleasant-smelling massage. A few double blind studies in the field of clinical psychology relating to the treatment of severe dementia have been published. Essential oils have a demonstrated efficacy in dental mouthwash products.
Aromatherapy has been also promoted for its ability to fight cancer; however, according to the American Cancer Society, "available scientific evidence does not support claims that aromatherapy is effective in preventing or treating cancer".