Smell training or olfactory training is the act of regularly sniffing or exposing oneself to robust aromas with the intention of regaining a sense of smell. The stimulating smells used are often selected from major smell categories, such as aromatic, flowery, fruity, and resinous. Using strong scents, the patient is asked to sniff each different smell for a minimum of 20 seconds, no less than two times per day, for three to six months or more. It is used as a rehabilitative therapy to help people who have anosmia or post-viral olfactory dysfunction, a symptom of COVID-19. It was considered a promising experimental treatment in a 2017 meta-analysis.