Along with olfactory implants, smell training is a promising but experimental treatment option.Several individual studies have indicated that smell training can increase olfactory sensitivity. In 2021 a meta-analysis was published that examined research studies of olfactory training for treating loss of smell as a consequence of a viral infection. It found clinically significant improvements and supported its use as a treatment option. As of March 2021, there have been no studies of smell training's efficacy for children.In 2017, the International and European Rhinologic Societies recommended smell training for treating loss of smell due to various conditions. In 2020, the British Rhinological Society published consensus guidelines for the treatment of smell loss due to COVID-19. Although no specific studies were available at that time, the expert panel made recommendations regarding treatment options and concluded that "olfactory training was recommended for all [COVID-19] patients with persistent loss of sense of smell of more than 2 weeks duration."Critics such as Richard Doty have pointed to the small sample sizes in the studies and the potential for the observed improvements to have been the result of nerve regeneration that would have occurred without intervention as reason to be skeptical.