Introduction
Influenza (the flu) is a contagious illness that affects the respiratory tract. Most people recover without needing emergency care, but the flu can sometimes lead to serious complications. Knowing which symptoms can be managed at home, when to contact a healthcare provider, and when to seek emergency care can help prevent delays in treatment—especially for people at higher risk.
What Is the Flu?
The flu is caused by a virus that infects the respiratory tract and spreads from person to person through virus-containing droplets released when an infected person coughs or sneezes. Common symptoms include fever, chills, cough, sore throat, body aches, headache, fatigue, and a runny or stuffy nose. Symptoms often begin suddenly. Not everyone with the flu will have a fever.
For most otherwise healthy people, the illness is not an emergency and recovery occurs with rest, fluids, and symptom management at home.
Who Is at Higher Risk for Flu Complications?
Certain groups are more likely to develop serious flu-related complications:
- Adults aged 65 and older
- Young children
- Pregnant individuals
- People with chronic medical conditions
- People with weakened immune systems
People in these groups are advised to contact a healthcare provider early if they develop flu symptoms.
Common Flu Symptoms
Flu symptoms may include:
- Fever or feeling feverish
- Chills
- Cough
- Sore throat
- Runny or stuffy nose
- Muscle or body aches
- Headache
- Fatigue
Symptom severity varies, and not everyone experiences all symptoms.
When to See a Doctor
Medical care outside the emergency room is often appropriate when symptoms are mild or moderate.
You should contact a primary care provider or urgent care if:
- You are in a higher-risk group and develop flu symptoms
- You are concerned about your illness
- Symptoms are uncomfortable but not severe
Antiviral medications may be prescribed by a healthcare provider and are most effective when started early in the illness, particularly for people at higher risk of complications.
When to Go to the Emergency Room for the Flu
Emergency care is recommended for people who are very sick or who develop emergency warning signs, including:
- Difficulty breathing or shortness of breath
- Persistent pain or pressure in the chest or abdomen
- Confusion or inability to stay awake
- Severe or persistent vomiting
- Signs of severe dehydration (such as very dark urine or confusion)
- Flu symptoms that improve and then suddenly return or worsen
Emergency Warning Signs by Age Group
Adults
Adults should seek emergency care if they experience:
- Trouble breathing or shortness of breath
- Persistent chest or abdominal pain
- New confusion or inability to stay awake
- Severe weakness or unsteadiness
Children
Children may need emergency care if they develop:
- Bluish lips or face
- Fast or labored breathing
- Severe headache or stiff neck
- Inability to take in fluids
- Signs of dehydration
- Symptoms that improve and then worsen
Infants
Emergency warning signs in infants include:
- Any fever in infants younger than 12 weeks
- Few or no wet diapers
- No tears when crying
- Inability to eat
- Inconsolable crying or marked irritability
Flu Complications Supported by High-Quality Evidence
Pneumonia
Pneumonia is a serious flu complication and can be life-threatening, especially in older adults. Flu-related pneumonia may develop during the illness and requires prompt medical evaluation.
Dehydration
Dehydration can occur due to fever, vomiting, or reduced fluid intake and may require emergency care if severe.
Worsening of Chronic Medical Conditions
The flu can worsen existing chronic conditions, increasing the risk of severe illness and hospitalization.
Prevention and Risk Reduction
Preventing the flu reduces the risk of severe illness and complications. Evidence-based prevention measures include:
- Receiving a seasonal flu vaccine
- Washing hands regularly
- Staying home when sick
- Covering coughs and sneezes
- Wearing a mask when appropriate to reduce spread
Frequently Asked Questions
How long does the flu usually last?
Many people begin to feel better after several days, though complete recovery may take one to two weeks.
When is the flu contagious?
People with the flu are most contagious during the first three days of illness. Some individuals, including young children and people with weakened immune systems, may be contagious for longer.
Can untreated flu become dangerous?
Yes. The flu can lead to serious complications such as pneumonia, dehydration, or worsening of chronic medical conditions.
When should I go to the ER for the flu?
Emergency care is recommended if you have severe symptoms such as breathing problems, confusion, severe dehydration, or symptoms that worsen after initially improving.
Should I go to the hospital for flu symptoms?
There is no high-quality evidence supporting hospital care for mild flu symptoms. Hospital or ER care is recommended when emergency warning signs are present.
What complications can occur after the flu?
High-quality evidence supports pneumonia, dehydration, and worsening of chronic medical conditions. Other complications lack sufficient evidence in this review.
Is trouble breathing after the flu serious?
Yes. Difficulty breathing is an emergency warning sign and requires immediate medical evaluation.
Key Takeaways
- Most people recover from the flu at home without emergency care.
- Certain groups are at higher risk for serious complications and should contact a healthcare provider early.
- Emergency care is necessary when severe warning signs are present, especially breathing problems or confusion.
- Pneumonia, dehydration, and worsening of chronic conditions are the flu complications supported by high-quality evidence.
APA Reference List
Centers for Disease Control and Prevention. (2024, August 13). About influenza. https://www.cdc.gov/flu/about/index.html
Centers for Disease Control and Prevention. (2024, August 26). Signs and symptoms of flu. https://www.cdc.gov/flu/signs-symptoms/index.html
Centers for Disease Control and Prevention. (2024, August 30). Flu: What to do if you get sick. https://www.cdc.gov/flu/takingcare/index.html
Centers for Disease Control and Prevention. (2024, September 11). People at increased risk for flu complications. https://www.cdc.gov/flu/highrisk/index.htm
Centers for Disease Control and Prevention. (2024, September 17). How flu spreads. https://www.cdc.gov/flu/spread/index.html
Centers for Disease Control and Prevention. (2025, September 26). Preventing seasonal flu. https://www.cdc.gov/flu/prevention/index.html
Centers for Disease Control and Prevention. (2025, November 20). Treating flu with antiviral drugs. https://www.cdc.gov/flu/treatment/antiviral-drugs.html
Cedars-Sinai. (n.d.). Flu: When to go to the ER. https://www.cedars-sinai.org/stories-and-insights/expert-advice/go-er-for-flu
EmergencyPhysicians.org. (n.d.). Flu — Know when to go to the ER. https://www.emergencyphysicians.org/article/know-when-to-go/flu
MedlinePlus. (2017, January 2). Acute bronchitis. https://medlineplus.gov/acutebronchitis.html
MedlinePlus. (2023, December 8). Pneumonia. https://medlineplus.gov/pneumonia.html
MedlinePlus. (2025, January 17). Earache. https://medlineplus.gov/ency/article/003046.htm
MedlinePlus. (2025, June 29). Sinusitis. https://medlineplus.gov/sinusitis.html
MedlinePlus. (2025, July 1). Your baby and the flu. https://medlineplus.gov/ency/article/007444.htm
UChicago Medicine AdventHealth. (n.d.). When is the flu an emergency? https://www.uchicagomedicineadventhealth.org/blog/when-flu-emergency