Imagine not being able to taste your morning coffee or smell the lemon you just cut. For some people with COVID-19, this is a reality. And it doesn't just happen to those with COVID-19, it is a common symptom of upper respiratory viruses.
The loss of taste and smell often go hand-in-hand. To understand why these impact each other, it’s important to first understand how taste and smell work. Your ability to smell comes from sensory cells, called olfactory sensory neurons, which are found in a small patch of tissue high inside your nose. Smells reach the olfactory sensory neurons through your nostrils and through a channel that connects the roof of your throat to your nose. These cells connect directly to the brain where smell is identified.
Chewing food releases aromas that access the olfactory sensory neurons. If the channel is blocked, such as when your nose is stuffed up by a cold, odors can’t reach the sensory cells that are stimulated by smells. As a result, you lose your ability to enjoy a food’s flavor. In this way, your senses of smell and taste work closely together.
Without the olfactory sensory neurons, familiar flavors such as chocolate or oranges would be hard to distinguish. Without smell, foods tend to taste bland and have little or no flavor. Some people who go to the doctor because they think they’ve lost their sense of taste are surprised to learn that they’ve lost their sense of smell instead.
Your sense of smell is also influenced by something called the common chemical sense. This sense involves thousands of nerve endings, especially on the moist surfaces of the eyes, nose, mouth and throat. These nerve endings help you sense irritating substances, such as the tear-inducing power of an onion or the refreshing coolness of menthol.
Now, for those with COVID-19, the loss of taste and smell is a common symptom. Many people with a mild case of COVID-19 regain their sense of taste and smell within four weeks. Those with more intense symptoms often have longer side effects.
Due to the complexity of COVID-19, it is difficult to determine a treatment. However, we know that post-viral olfactory dysfunction (PVOD) is the most common cause of smell disorders. Since COVID-19 is a virus, treatment used for PVOD could be helpful. We use olfactory training to treat PVOD.
Olfactory training is a process that involves repeatedly smelling different things. This stimulates the olfactory system and establishes memory of that smell. Olfactory training is most effective when done as soon as possible; usually when smell does not come back after one month, but it can be started earlier. Here are some steps you can take at home to help.
Olfactory training instructions:
- Begin with four scents, such as rose (floral), lemon (citrus), cloves (spicy) and eucalyptus (resinous). You can purchase these scents in the form of essential oils online or from local health food, aromatherapy, specialty pharmacy or craft stores.
- Hold the essential oil in front of your nose. Gently inhale for 10 to 20 seconds and focus on the memory of the smell.
- Take a few breaths before moving onto the next fragrance.
- Repeat two to four times a day for at least three months.
- After three months, change the fragrances from each category and repeat the process. Examples of other fragrances include:
- Floral: gardenia, jasmine, lavender
- Citrus: tangerine, orange, lime, lemongrass
- Spicy: thyme, rosemary, ginger, cinnamon
- Resinous: frankincense, myrrh, balsam
For some, the sense of taste or smell may not return completely, or at all. And, as the sense of smell comes back, it could be distorted--things that should smell good might smell bad at first. Unfortunately, there is no cure, but we encourage you to discuss any questions you have with your primary care provider.
- Boscolo-Rizzo, P. et al. (2020). Evolution of Altered Sense of Smell or Taste in Patients with Mildly Symptomatic COVID-19. JAMA Otolaryngology-Head & Neck Surgery, 146(8):1-5.
- Choi, BY, Jeong, H, Noh, H, Park, JY, Cho, JH, Kim, JK. (2021). Effects of Olfactory Training in Patients with Postinfectious Olfactory Dysfunction. Clinical and Experimental Otorhinolaryngology, 14(1): 88-92.
- Patel, ZM, Wise, SK, DelGaudio, JM. (2017). Randomized controlled trial demonstrating cost-effective method of olfactory training in clinic practice: essential oils at uncontrolled concentration. Laryngoscope Investigative Otolaryngology, 2(2): 53-56
- Soler, ZM, Patel, ZM, Turner, JH, Holbrook, EH. (2020). A primer on viral-associated olfactory loss in the era of COVID-19. International Forum of Allergy & Rhinology, 10(7): 814-820.
- Zhang, Y, Mei, T, Chen, Y, Wang, L, Jiang, L, Liu, K, Zhao, L, Leuo, Z, Chi, W, Zhu, X. (2021). Smell disorders in COVID-19 patients: Role of olfactory training. A protocol for systematic review and meta-analysis. Medicine, 100:8(e24862).