How does COVID-19 cause all those symptoms?

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Image shows an African American woman sitting on a couch looking down at a thermometer. She's wrapped in a blanket and looks tired.

People have experienced a wide variety of symptoms from COVID-19. Some feel like they have a mild cold, while others feel exhausted. Some develop a lingering cough, while others lose their sense of smell and taste. In extreme cases, some people require hospitalization. And, unfortunately, some people die.

Scientists haven’t yet figured out why COVID-19 presents with such a wide range of symptoms or why different people experience vastly different symptoms. But we do know why the virus causes individual symptoms as it attacks our cells and as our immune system works to fight it off.

Common COVID-19 symptoms and their causes

Shortness of breath: People experience shortness of breath when COVID-19 (or your immune system’s response to it) damages the lungs. Inside the lungs, the body absorbs oxygen (when you inhale) and expels carbon dioxide (when you exhale) through millions of tiny air sacs called alveoli. When the virus invades cells in lung tissue – or when your immune system intervenes to attack the virus – the lung tissue can become swollen, and those air sacs can fill with fluid. When the alveoli fill with fluid, breathing is harder and people can feel short of breath.

Loss of smell and taste: A unique symptom of COVID-19 is a partial or total loss of sense of smell. In 2020, scientists discovered this symptom is caused by the virus damaging cells in the nose that help transfer signals to the brain about odors. Sense of taste is closely related to sense of smell, so when the sense of smell is affected, so is the sense of taste. Although this symptom has been commonly reported, studies show that loss of smell and taste is less common with the Omicron variant.

Image shows a sick young woman lying on the couch and holding her head with hand.

Fatigue: It’s not entirely clear how COVID-19 causes fatigue. Fatigue as a symptom can be linked to many different conditions. In patients with COVID-19, fatigue could have to do with cell damage due to infection, respiratory issues like pneumonia or the over-exertion of your immune system as it fights the virus.

Brain fog: Feeling mentally sluggish or slow is another symptom that scientists don’t yet fully understand. One possibility is that brain fog arises from damage the virus does to the brain directly. It’s also possible that brain fog is a result of sleep deprivation, depression, anxiety, fatigue, and other conditions related to being sick, in general. Different people experience brain fog for different reasons.

Gastrointestinal issues: Some people with COVID-19 experience gastrointestinal issues, such as diarrhea and vomiting. This is because the virus can invade the cells in the intestines. Like the effects in the lungs and respiratory tract, the intestinal tissue can become irritated, leading to those gastrointestinal issues.

Stuffy nose: When the COVID-19 virus invades and copies itself inside our cells, those cells can become damaged and inflamed. In our nose, that damage and inflammation makes us feel stuffed up. We also create more mucus in an attempt to fight off the virus’s invasion, leading to a runny nose.

Sore throat: Like in other parts of your body, as your immune system fights off a COVID-19 infection, tissue becomes swollen. In your throat, this inflammation of your tonsils and other parts of the throat can be painful.

Fever: The fever you might have when you’re sick with COVID-19 is a result of your immune system being in fighting-mode. In response to a virus like the one that causes COVID-19, your immune system triggers the body’s temperature to rise, which helps your body create the immune cells it needs to fight the virus. A fever means your immune system is working to attack the virus, but sometimes a fever can become dangerous. If a fever reaches 103 F or higher, call your healthcare provider or visit an urgent care clinic.

Image shows a white man checking on his sick child who is lying on a couch.

COVID-19 symptoms and long COVID

For most people with COVID-19, these symptoms will clear up within a couple of weeks. However, about 20-30% of people experience lingering symptoms, such as fatigue, trouble breathing or loss of smell or taste for months. The Centers for Disease Control and Prevention (CDC) recently released a report showing that one in five adults may experience some kind of health issue after having COVID-19. These issues range from blood blots to heart problems to kidney failure.

Someone who experiences symptoms for longer than a month after recovering from their initial infection has a condition called long COVID. The CDC reported that although long COVID symptoms are more common in people who have had a severe infection, anyone, regardless of the severity of their disease, can continue to experience symptoms.

Medical experts aren’t sure why long COVID develops, but more research is being done every day.

Staying safe

To keep yourself safe from COVID-19, get all the recommended vaccine doses for which you are eligible and consider wearing a mask in indoor spaces. Although vaccinated people can get COVID-19, they’re much less likely to become severely ill, require hospitalization or die. If you’re looking for a place to get a COVID-19 vaccine, check out this list of vaccination locations around Oregon.