Cold and Flu Complications: How Dangerous Are These Illnesses?

Even a mild cold or bout of influenza can compromise your immune system and lead to other health concerns.

Medically Reviewed
a doctor checking a patient for flu complications
A cold or the flu can reduce your body’s ability to fight off other infections.Getty Images

Most cases of a cold or the flu can be treated at home, with symptoms going away within a week or two. But infections of the upper respiratory tract (nose and throat) and lower respiratory tract (lungs) can lead to moderate or potentially serious health complications.

The Centers for Disease Control and Prevention (CDC) estimates that in the United States, the flu has resulted in between 140,000 and 810,000 hospitalizations each year since 2010 and between 12,000 and 61,000 deaths. (1) While most people with a common cold get better in about a week, those with weakened immune systems, asthma, or respiratory conditions can develop serious complications such as bronchitis or pneumonia, says the CDC (2).

Feeling mildly sick, then better, and then sick again could be a sign of a secondary bacterial infection, a condition that can occur when your immune system is weakened from a mild illness.

“It could be that the immune system got tired and another infection was able to come in,” says David Weitzman, MD, an urgent care physician in South Carolina and a board member of the American Academy of Urgent Care Medicine. “Or you were exposed to a second type of virus or bacteria and got sick again.”

RELATED: The Flu: Self-Treat, See a Doctor, or Go to the ER?

Who Is Most at Risk for Cold and Flu Complications?

Certain populations are especially at risk of developing cold- or flu-related complications:

  • Adults Age 65 and Older People in this age group account for between 50 to 70 percent of seasonal flu-related hospitalizations and between 70 and 85 percent of seasonal flu-related deaths, according to the CDC. (3)
  • Children Under 5 Millions of children get sick with seasonal influenza every year, and thousands require hospitalization; some die. (4)
  • Pregnant Women Changes to the immune system, heart, and lungs during pregnancy can raise the risk of severe illness from the flu. The flu may also be harmful to a developing baby. (5)
  • Adults With Preexisting Conditions This includes chronic illnesses such as asthma, chronic obstructive pulmonary disease, heart disease, diabetes, and HIV or AIDS. (6)
  • American Indians and Alaska Natives Research has shown that these groups experience a disproportionate number of influenza-related hospitalizations compared with the general U.S. population. (7)

RELATED: 8 Home Remedies to Stop a Bad Cough

What Complications Can a Cold or the Flu Cause?

Potential complications of colds and flu include the following:


Bronchitis, an inflammation of the airways that bring air to and from the lungs, is commonly caused by viruses that cause colds and the flu, according to the National Heart, Lung, and Blood Institute. Bacteria and inhaled irritants can also cause bronchitis. The most common symptom is mucus-laden coughing, with other symptoms including shortness of breath and wheezing. (8)


Colds and the flu can decrease appetite and liquid intake, making it easy to become dehydrated. Diarrhea, vomiting, and fever can also contribute to dehydration, according to the Mayo Clinic (9).

Signs of dehydration in infants or young children may include listlessness, no wet diapers for three hours, a dry mouth and tongue, and no tears when crying. Adults may develop extreme thirst, urinate less, produce darker-colored urine, or feel dizzy, confused, or fatigued. (9)

Severe dehydration is a medical emergency and may require treatment with intravenous fluids. (9)

Ear Infection

“With a cold, you can get ear pain because the eardrum gets inflamed by the viral infection,” says Richard Rosenfeld, MD, a professor and the chair of otolaryngology at the State University of New York Downstate Health Sciences University in Brooklyn. Ear infections are more common in children because the Eustachian tubes (passageways that drain fluids out of the ear) are smaller and can easily become swollen or blocked.


An inflammation of the middle layer of the heart’s wall (myocardium), myocarditis can be caused by cold or flu viruses, according to the Mayo Clinic. It may begin with mild symptoms, such as fatigue or shortness of breath, but it can lead to arrhythmia (rapid or abnormal heart rhythms), heart attack, or stroke. (10)


Viral infections like influenza can cause inflammation that damages muscle fibers, a condition called infectious myositis, according to Harvard Health. Although it can cause muscle aches and muscle tenderness, the main symptom is weakness. Myositis can subside on its own in a few days or weeks, or it can become a chronic condition. (11)


An inflammation of the saclike tissue surrounding the heart (pericardium), pericarditis is commonly caused by viral infections, according to the American Heart Association. Symptoms include sharp chest pain resembling a heart attack accompanied by fever, weakness, and coughing. Most of the time, the condition resolves itself with little or no treatment, but severe cases require hospitalization and surgery. (12)


Cold and influenza viruses can lead to pneumonia, a common and potentially life-threatening lung infection. These viruses can lead to viral pneumonia or bacterial pneumonia, the latter of which is usually more serious, according to the American Lung Association. (13)

Symptoms of pneumonia include cough, fever, shortness of breath, rapid and shallow breathing, and nausea and vomiting (especially in small children). If untreated, pneumonia can become severe, with signs such as difficulty breathing, rapid heart rate, and a bluish tint to the lips and nail beds, according to the American Lung Association. (14)

Sinus Infection

Acute sinusitis, an inflammation of the sinuses that causes a buildup of mucus, is most often caused by a cold, according to Harvard Health. The most common symptoms are congestion, headache and facial pain, and discolored mucus, with other signs including loss of smell or taste, cough, bad breath, fever, toothache, and fullness in the ears. (15)

RELATED: No Flu Shot and Now You Have the Flu: What to Do

Are All Complications of a Cold or Flu the Same?

While both a cold and the flu can cause complications such as sinus and ear infections, complications from the flu are generally more serious and are more likely to lead to conditions that may require hospitalization, like pneumonia, according to the CDC. (16)

Learn More About How to Tell the Difference Between a Cold and the Flu

Can Cold or Flu Treatment Cause Complications?

While over-the-counter pain relievers and fever reducers can lessen the symptoms of a cold and the flu, there can be complications.

For instance, taking too much Tylenol (acetaminophen) can damage the liver. According to the Cleveland Clinic, the daily adult dose should not exceed 4 grams per day; for people with liver conditions, the limit is 2 grams per day. (17)

The use of aspirin to reduce pain and fever has been associated with a risk of Reye’s (also called Reye) syndrome in children and teenagers who have a viral infection such as the flu. Reye’s syndrome is a rare but serious condition that causes swelling of the brain and liver damage, according to the Mayo Clinic. (18)

Prescription antiviral drugs for treating the flu may have side effects. The most common side effects of Tamiflu (oseltamivir), for instance, are nausea and vomiting. (19)

When Should I Seek Medical Help?

Anyone can develop serious complications from the flu, but certain people are at an especially high risk, including men and women over age 65, those with certain chronic health conditions (such as asthma, diabetes, or heart disease), pregnant women, and children younger than 5 (especially those under 2).

The CDC lists a number of emergency warning signs of the flu. For adults, these include the following symptoms: (20)

  • Trouble breathing or shortness of breath
  • Persistent pain or pressure in the chest or abdomen
  • Persistent dizziness, confusion, or inability to rouse from sleep
  • Seizures
  • Not urinating
  • Severe muscle pain
  • Severe weakness or unsteadiness
  • Fever or cough that improves but then returns or worsens
  • Worsening of chronic medical conditions with fever and a worse cough

Emergency warning signs for children with the flu include these:

  • Fast breathing or trouble breathing
  • Bluish lips or face
  • Ribs pulling in with each breath
  • Chest pain
  • Severe muscle pain (child refuses to walk)
  • Dehydration (no urine for eight hours, dry mouth, no tears when crying)
  • Not alert or interacting when awake
  • Seizures
  • Fever above 104 degrees; in children younger than 12 weeks, any fever
  • Fever or cough that improves but then returns or worsens
  • Worsening of chronic medical conditions

RELATED: How Do You Handle a Flu Emergency?

What Happens if the Flu Is Not Treated?

Most people with the flu recover in a few days to a few weeks without medical care or prescription antiviral drugs, says the CDC. But if your symptoms are severe or you’re in a high-risk group, going without treatment could have serious and potentially life-threatening consequences. Don’t delay: Antiviral medications are most effective when you begin taking them within the first two days of feeling sick, says the CDC. (21)

Additional reporting by Pamela Kaufman.

Editorial Sources and Fact-Checking

  1. Disease Burden of Influenza. Centers for Disease Control and Prevention. April 17, 2020.
  2. Common Colds: Protect Yourself and Others. Centers for Disease Control and Prevention. February 11, 2019.
  3. People 65 Years and Older and Influenza. Centers for Disease Control and Prevention. November 21, 2019.
  4. Children and Influenza (Flu). Centers for Disease Control and Prevention. October 23, 2019.
  5. Pregnant Women and Influenza. Centers for Disease Control and Prevention. December 20, 2019.
  6. People at High Risk for Flu Complications. Centers for Disease Control and Prevention. August 27, 2018.
  7. Gounder PP, Callinan, LS, et al. Influenza Hospitalizations Among American Indian/Alaska Native People and in the United States General Population. Open Forum Infectious Diseases. March 2014.
  8. Bronchitis. National Heart, Lung, and Blood Institute.
  9. Dehydration. Mayo Clinic. September 19, 2019.
  10. Myocarditis. Mayo Clinic. March 16, 2019.
  11. Myositis. Harvard Health. March 2019.
  12. What Is Pericarditis? American Heart Association. March 31, 2016.
  13. What Causes Pneumonia? American Lung Association. February 27, 2020.
  14. Pneumonia Symptoms and Diagnosis. American Lung Association. February 27, 2020.
  15. What to Do About Sinusitis. Harvard Health. January 29, 2020.
  16. Common Cold. Centers for Disease Control and Prevention. February 6, 2020.
  17. The Common Cold and the Flu: Management and Treatment. Cleveland Clinic. August 2, 2016.
  18. Reye’s Syndrome. Mayo Clinic. August 8, 2018.
  19. What You Should Know About Flu Antiviral Drugs. Centers for Disease Control and Prevention. April 22, 2019.
  20. Flu Symptoms and Complications. Centers for Disease Control and Prevention. September 18, 2019.
  21. Flu: What to Do if You Get Sick. Centers for Disease Control and Prevention. October 8, 2019.
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