A common cold frequently causes a temporary reduction in the ability to smell and, consequently, a perceived loss of taste. This symptom is often expected during an upper respiratory infection. The medical term for a complete loss of smell is anosmia, while the loss of the ability to taste is called ageusia. Most colds only cause a partial reduction in these senses, which is a temporary and common experience when dealing with congestion.
How Colds Affect Olfactory Function
The primary mechanism by which a cold diminishes smell is physical obstruction within the nasal cavity caused by inflammation. When a cold-causing virus infects the upper respiratory tract, the body initiates an inflammatory process. This response involves swelling of the mucous membranes lining the nasal passages.
Swelling, combined with excessive mucus production, physically blocks the pathway scent molecules must travel. Odor molecules enter the nose and must reach the olfactory epithelium, a specialized tissue located high up in the nasal cavity. Inflammation and congestion prevent these molecules from reaching the olfactory receptors, leading to a temporary inability to detect smells.
This type of smell loss is classified as a conductive loss because odor signals cannot be conducted to the sensory cells. It is not due to direct damage to the olfactory nerve, but rather a mechanical blockage. As inflammation subsides and congestion clears, the physical blockage is removed, allowing odor molecules to reach the receptors.
The Difference Between Taste and Flavor
The feeling that food is bland or tasteless during a cold is a common misconception about the sense of taste. True taste, or gustation, is limited to five basic qualities: sweet, sour, salty, bitter, and umami. These basic tastes are detected by taste buds located primarily on the tongue.
A cold rarely affects the function of these taste buds, meaning you can still distinguish between basic tastes. What people describe as “taste” is actually flavor, a complex sensation created by the brain. Flavor is a combination of true taste and smell, with smell contributing 75% to 95% of the overall perception.
When food is chewed, aromatic molecules are released and travel through a passage connecting the throat to the nasal cavity, a process known as retronasal olfaction. Since nasal passages are blocked by congestion during a cold, these aromatic molecules cannot reach the olfactory receptors. The brain only receives basic taste information from the tongue, making complex foods taste uniform.
Duration and When Loss of Senses Becomes Concerning
For a common cold, the loss of smell is temporary and resolves as congestion improves. Most people find their sense of smell returns fully within 7 to 10 days, coinciding with the clearance of the cold. In some cases, the full return of the sense may lag slightly behind the resolution of physical symptoms.
If the loss of smell persists beyond two weeks after cold symptoms have cleared, a medical evaluation may be necessary. Persistent post-viral anosmia can occur, though it is less common with a typical cold. Seeking professional advice is important if the loss of smell occurs suddenly without preceding congestion or other cold symptoms.
A sudden, isolated loss of smell or taste, even without nasal congestion, became a recognized symptom of COVID-19 infection. If a complete loss of these senses occurs, or if symptoms are accompanied by other signs like a high fever or shortness of breath, testing and medical consultation are advised. Smell loss from COVID-19 can sometimes be longer than that from a common cold, occasionally lasting for weeks or months.