Smell retraining therapy (SRT) is a treatment for loss of smell, also referred to as hyposmia or anosmia. It can be used to help return your sense of smell if it was lost during a viral infection or minor head trauma. SRT was originally developed in 2009 by Dr. Thomas Hummel at the University of Dresden.
The process of SRT involves the repeated presentation of different smells through the nose to stimulate the olfactory system and establish memory of that smell. It is best to start with at least four different scents, especially smells you remember. The most recommended fragrances are rose (floral), lemon (fruity), cloves (spicy), and eucalyptus (resinous). Take sniffs of each scent for 10 to 20 seconds at least once or twice a day. While sniffing, it is important to be focused on the task. Try to concentrate on your memory of that smell. After each scent, take a few breaths and then move on to the next fragrance. It is recommended that you do this for at least 12 weeks (three months), but you can do it longer, alternating the scents if you like.
SRT is believed to work as a combination of the unique ability for smell nerves to regrow while encouraging improved brain connectivity. Either way, try not to get discouraged; it is common for this process to take some time before you start to smell anything, and that is okay.
Most people can identify the five different tastes that humans are capable of detecting: salty, sweet, bitter, sour, and savory (umami). Some researchers have also tried to categorize the many different smells as well. These categories include floral, fruity, spicy, resinous, burnt and foul. Instead of having to practice smelling burnt or foul odors, SRT concentrates on the more pleasant smells from the other four categories.
Most of the studies on SRT have been done on patients with post-viral (i.e., after a cold or upper respiratory infection) smell loss. Research findings on SRT for COVID-19-related smell loss are not yet available. It seems that most people get their sense of smell back within several months after COVID-19. If you are not in that group, it may be beneficial to consider trying SRT. Even if it is not helpful, it will not worsen the problem.
Many people prefer to use essential oils. These can be purchased online or from local health food, aromatherapy, or craft stores. These can be the most convenient because they have a long shelf-life, but you can also use a variety of other options including inhalant sticks or fresh fruits and herbs. When using the oils, you can place a small amount into a glass jar with a lid. Remember to close the lid tightly after each use to preserve the smell into the jar.
A study conducted by researchers at Stanford University showed that SRT worked better when paired with sinus rinses that included steroids1. Consult an ENT (ear, nose, and throat) specialist, or otolaryngologist, to see whether this treatment may be a better option for you.
1 Nguyen TP, Patel ZM. Budesonide irrigation with olfactory training improves outcomes compared with olfactory training alone in patients with olfactory loss. Int Forum Allergy Rhinol. 2018 Sep;8(9):977-981.