Updated on October 16, 2024.
When COVID-19 first emerged in late 2019 and early 2020, the disease was best known for its respiratory symptoms. But scientists around the world have since learned that the virus (formally known as SARS-CoV-2) doesn’t only attack the lungs. COVID can also cause damage to the heart, the kidneys, as well as the brain and the central nervous system.
COVID and neurological symptoms
The most widely known neurological symptom associated with COVID is the loss of one’s sense of smell or taste. (Neurological refers to the nervous system.) Several other symptoms related to the brain and nervous system have also been linked to COVID.
In extreme cases, when a person has severe illness from COVID and is hospitalized, they may experience damage to the lungs or other organs, as well as strokes from blood clots. These issues can reduce how much oxygen is available to the brain, which can be very damaging to the brain.
Inflammation caused by the infection can also cause bleeding or swelling in the brain or spinal cord, which can lead to sensory symptoms, weakness, or even paralysis from Guillain-Barré syndrome (GBS). (GBS occurs when the immune system attacks nerves in the body.)
Most cases of neurological symptoms from COVID are less extreme than these, but they can still be stressful or even debilitating. Many neurological symptoms are linked to Long COVID, the term for the range of symptoms that can arise and linger long after an initial COVID infection.
Why the brain is affected by COVID
Serious viral infections often affect the central nervous system. This can happen directly if the virus damages the blood-brain barrier. (The blood-brain barrier is a protective structure that helps shield the brain from potentially harmful substances that circulate in the bloodstream, including germs.)
Damage from COVID can also happen indirectly, by causing other health issues that affect the nervous system and brain. For example, inflammation triggered by the immune system’s response to SARS-CoV-2 may lead to swelling or bleeding in the brain or spine, which can cause neurological issues.
Here’s what is known about the most common neurological symptoms caused by acute COVID infections and Long COVID, as well as some cognitive symptoms (those related to thinking or mental processing).
Loss of smell or taste
A common feature of a COVID infection is anosmia, or the sudden loss of the sense of smell. (One’s sense of taste often goes with smell, since the two are connected.)
A 2023 study published in The Laryngoscope found that in 2021, of the 35.8 million adults in the United States who were diagnosed with COVID, more than 60 percent reported a loss of smell or taste.
This neurological effect can develop days before a cough, fever, or other symptoms set in. Most people regain their senses of smell or taste soon after recovering from the virus. But in up to 25 percent of cases, these senses returned only partially, or not at all, according to the study. For some people, the loss of smell or taste has been known to continue for years.
Researchers are still investigating the cause of anosmia, but one theory is that it may be due to inflammation affecting with the body’s sensory signaling systems.
Headaches
Some people experience new mild to severe headaches with a COVID infection. These can continue if a person has Long COVID.
COVID-related headaches might feel like migraines that appear on both sides of the head and they may last much longer than regular headaches. These headaches can persist for weeks and involve extreme spikes in pain.
There are several theories for why these headaches happen. The virus may trigger and irritate the trigeminal nerve, which is responsible for sending pain messages from the face to the brain.
COVID can also cause the blood to be more prone to clotting. Big clots can cause big problems, including heart attacks and strokes. But microclots (tiny clots in the smallest blood vessels known as capillaries), may contribute to brain fog and other issues. Some researchers believe that COVID-related headaches may be caused by blood clots in the venous sinuses, the blood vessels that surround the brain.
Neuropathy
Numbness, burning, pain, or prickling sensations in various parts of the body can indicate damage to the nerves, a condition known as neuropathy. These symptoms are also linked to COVID.
Neuropathic pain was experienced by 6.7 percent of people hospitalized with COVID and by 34 percent of people with Long COVID, according to a 2023 systematic review and meta-analysis published in the Journal of Clinical Medicine. Some researchers believe these effects are caused by the virus affecting the nerves that regulate and send signals of pain, pressure, touch, heat, and cold to the brain.
Neurodegenerative conditions
A COVID infection could also be linked to new cases of neurodegenerative conditions, like Parkinson’s disease or Alzheimer’s disease, in people who hadn’t been showing signs of these conditions before. (Neurodegenerative refers to the deterioration of brain and nervous tissue over time.) Some researchers theorize that the virus might damage the central nervous system and speed up an already-present neurodegenerative disease that wasn’t yet obvious.
The relationship between the infection and neurodegenerative diseases still has no direct link, according to a 2024 article published in Frontiers in Neurology. The researchers noted that chronic inflammation and a heightened immune response that are typical of Long COVID may contribute to a variety of negative effects on the brain, both direct and indirect, in ways that are yet to be confirmed.
Brain fog
Some people with COVID experience what’s known as brain fog, a cognitive effect similar to that caused by a concussion. Brain fog may involve issues with memory and attention. It can last for many months, even if a person’s original symptoms of the virus were mild.
The reasons for brain fog are still not entirely clear to researchers, but they may be related to the body’s overactive immune response to COVID. This may cause the blood to clot excessively and lead to brain problems.
In addition to the effect that COVID may have on damaging the blood-brain barrier, some research suggests that SARS-CoV-2 may be able to cross the barrier and enter the brain directly. A 2024 study published in Nature Neuroscience found that this may lead to brain fog in people with Long COVID.
An estimated 40 percent of people with Long COVID also have sleep disturbances, according to the National Institute of Neurological Disorders and Stroke. Poor sleep can also lead to fatigue and difficulties with thinking.
Recognize serious warning signs
Most people, especially those who are up-to-date on their COVID vaccines, will experience only mild symptoms with a COVID infection. These include cough, fatigue, shortness of breath, fever, or sore throat.
But if you develop more serious symptoms, seek immediate medical attention. Emergency warning signs of COVID include:
- Trouble breathing
- Persistent pain or pressure in the chest
- New confusion
- Inability to wake or stay awake
- Discoloration to the lips, nail beds, or face (depending on skin tone, they may appear gray, pale, or blueish)
Warning signs of stroke or other brain involvement may include:
- Sudden drooping of the face
- Sudden weakness or numbness of the arm
- Sudden confusion or trouble speaking
- Vision loss in one or both eyes
- Loss of balance or coordination or difficulty walking
- Sudden and severe headache
If you develop any of these symptoms, call 911.
