COVID-19 most commonly causes sore throat, runny or stuffy nose, headache, and tiredness. Symptoms typically appear 3 to 4 days after exposure to current variants, though the window can range from 2 to 14 days. Most people recover within a week or two, but the infection can affect far more than just the respiratory system.
The Most Common Symptoms
The coronavirus produces a wide range of symptoms that overlap heavily with colds and the flu. The symptoms most people experience include sore throat, congestion or a runny nose, headache, fatigue, and cough (often dry). Fever, muscle aches, and sneezing are also common but don’t appear in every case.
Beyond the respiratory symptoms, COVID-19 frequently causes gastrointestinal problems. Diarrhea shows up in roughly 10% to 34% of patients, depending on the study. Nausea or vomiting affects 10% to 26% of patients, and abdominal pain occurs in about 9% to 15%. These gut symptoms sometimes appear before the more recognizable respiratory ones, which can make early identification tricky.
Loss of taste or smell was a hallmark of early pandemic strains but has become much less common. With the Omicron variant and its descendants, the rate of smell loss dropped two- to tenfold compared to earlier strains. Current estimates put it around 2% to 12% of infections, depending on genetic background. When it does occur, it often shows up without the usual nasal congestion that would explain it, which remains a distinguishing feature of COVID-19.
How Symptoms Differ From a Cold or Flu
Because COVID-19, the flu, and the common cold share so many symptoms, telling them apart by feel alone is difficult. A few patterns can help narrow it down, though testing is the only reliable way to confirm which virus you have.
Compared to a cold, COVID-19 is more likely to cause fatigue, headache, fever, and muscle aches. Colds almost never produce significant tiredness or body aches. Shortness of breath can occur with COVID-19 but essentially never with a cold. And loss of taste or smell, while less common than it used to be, still points toward COVID-19 rather than a cold.
The flu is harder to distinguish. Both infections commonly cause headache, sore throat, fatigue, and congestion. The biggest differences: flu almost always brings a fever, while COVID-19 only sometimes does. Flu also tends to cause more prominent muscle aches and a persistent cough. COVID-19 is more likely to cause loss of taste or smell, which is rare with the flu. The incubation period offers another clue. Flu symptoms hit fast, typically within 1 to 4 days, while COVID-19 currently averages 3 to 4 days but can take up to two weeks.
How the Virus Causes These Symptoms
The coronavirus enters your cells by latching onto a protein called ACE2, which sits on the surface of cells throughout your body, not just in your lungs. ACE2 is found in the lining of your nose, throat, gut, heart, and blood vessels. This is why COVID-19 can cause such a wide range of symptoms across different organ systems rather than staying confined to the airways.
Once attached, the virus uses enzymes on your cell surfaces to break through and get inside. It has a structural advantage that allows it to infect a broader variety of cell types than many other respiratory viruses. This broader reach, combined with the virus’s ability to partially hide from immune detection early on, can lead to a delayed immune response and a longer recovery period in some people.
Many Infections Cause No Symptoms at All
A significant number of people infected with SARS-CoV-2 never develop any symptoms. Recent data from pediatric populations found that roughly 60% of COVID-19 infections were completely asymptomatic. In adults, the rate varies but remains substantial, particularly among vaccinated individuals and those with prior infections. Asymptomatic carriers can still spread the virus, which is one reason COVID-19 proved so difficult to contain compared to infections where symptoms reliably appear before a person becomes contagious.
How Symptoms Progress Over Time
For most people, COVID-19 follows a predictable arc. Symptoms begin 3 to 4 days after exposure on average, though earlier variants had longer incubation periods (around 6.5 days for the original strain, 4.3 days for Delta). The illness typically peaks around days 3 to 5 after symptoms start and resolves within 7 to 10 days.
A small percentage of people experience a second wave of worsening around days 7 to 10, often marked by increasing shortness of breath. This pattern signals that the immune response itself is driving inflammation in the lungs, and it’s the point where mild cases can turn serious.
Symptoms That Require Emergency Care
Most COVID-19 infections resolve on their own, but certain warning signs indicate a medical emergency. Call 911 or go to an emergency room if you or someone you’re caring for develops:
- Trouble breathing that goes beyond mild congestion or occasional coughing
- Persistent chest pain or pressure
- New confusion or difficulty thinking clearly
- Inability to wake up or stay awake
- Pale, gray, or blue color in the lips, nail beds, or skin
That bluish or gray discoloration signals that blood oxygen has dropped dangerously low and the body isn’t getting enough air. It’s one of the most urgent signs of severe COVID-19.
Long COVID Symptoms
For some people, symptoms don’t resolve when the acute infection ends. Long COVID can involve more than 200 reported symptoms, but the most common are fatigue, brain fog (difficulty concentrating, memory problems, mental sluggishness), and post-exertional malaise, where physical or mental effort triggers a crash in energy and function that can last days.
Most people with lingering symptoms see significant improvement within 3 months. Others, however, may not improve for months or even years. Long COVID can follow even mild initial infections, and its severity doesn’t always correlate with how sick someone was during the acute phase.