Influenza, commonly referred to as the flu, is a widespread viral infection that primarily impacts the respiratory system, including the lungs, throat, nose, and airways. The illness typically arrives suddenly and can range in severity. While many recover in about one to two weeks, the flu can pose serious health risks for young children, older adults, and individuals with pre-existing health conditions.

Common Symptoms of Influenza

Body Aches and Muscle Pain One of the hallmark symptoms of the flu is generalized body pain, especially in the muscles and joints. These aches stem from the immune system’s response to the virus, which leads to inflammation throughout the body.

Persistent Cough A dry or productive cough often accompanies the flu. It serves as a mechanism for the body to clear out mucus and viral particles from the lungs and airways.

Severe Fatigue Extreme tiredness is frequently reported by those with the flu. This fatigue is due to the energy demands placed on the body by the immune response. Even after other symptoms subside, tiredness can persist for several days.

Fever and Chills A spike in body temperature, often reaching 100–104°F, is a sign that the body is actively fighting the infection. Chills and sweating may occur as the body attempts to regulate temperature.

Headache Headaches are another symptom triggered by the immune system. The body releases certain chemicals in response to infection that can cause inflammation, resulting in pain in the head.

Nasal Congestion or Runny Nose The flu virus can cause swelling of the tissues in the nasal passages, leading to a blocked or runny nose. While more associated with the common cold, nasal symptoms are also frequent in influenza cases.

Sore Throat A dry, painful throat may appear due to irritation caused by the virus entering through the mouth and nose. This symptom might be mild or absent in some cases.

Additional Symptoms in More Severe Cases

In certain individuals, especially those with compromised immune systems, the flu can cause complications beyond the respiratory system.

Ear Infections The virus can travel to the middle ear, causing pain, pressure, and sometimes fever. This is more common in young children.

Pneumonia When the virus reaches the lungs and causes inflammation in the alveoli, it can lead to pneumonia. Symptoms may include chest pain, difficulty breathing, low oxygen levels, and a worsening cough.

Sinus Infections Inflammation and fluid buildup in the sinuses may occur, resulting in pressure around the face, headaches, nasal congestion, and postnasal drip.

Rare but Serious Flu Complications

Although uncommon, certain complications of the flu can be life-threatening. These are more likely in vulnerable groups such as infants, seniors, pregnant individuals, and those with chronic health conditions.

Encephalitis This is an inflammation of the brain that may result in confusion, seizures, memory loss, muscle weakness, hallucinations, and difficulty speaking or understanding language. It requires immediate medical attention.

Multiple Organ Failure In severe cases, the flu can overwhelm the body's systems and lead to the failure of vital organs such as the kidneys, liver, or heart. Symptoms include extreme fatigue, swelling, weight loss, and loss of coordination.

Myositis and Rhabdomyolysis The flu can trigger muscle inflammation, leading to pain and weakness. In rare cases, this can develop into rhabdomyolysis—a breakdown of muscle tissue that releases harmful proteins into the bloodstream, potentially damaging the kidneys.

Myocarditis When the flu virus affects the heart, it can cause myocarditis, or inflammation of the heart muscle. This can result in chest pain, irregular heartbeat, swelling in the limbs, and even cardiac arrest in extreme cases.

Sepsis This is a serious bloodstream infection caused by an overactive immune response. It is a medical emergency and may cause rapid heart rate, fever, confusion, shortness of breath, and severe pain.

Flu Symptoms in Children

Children, particularly those under the age of two, are at increased risk of flu complications. In addition to common symptoms like fever, cough, and body aches, children may also experience nausea, vomiting, diarrhea, and earaches. They might appear irritable, sleep more than usual, or become unusually quiet or inactive.

How the Flu Spreads

Influenza is highly contagious and spreads through droplets expelled when an infected person coughs, sneezes, or talks. These droplets can land in the mouths or noses of people nearby. Although less common, the virus can also be picked up from contaminated surfaces.

When to Seek Medical Attention

For most individuals, flu symptoms can be managed at home with rest, fluids, and over-the-counter medication. However, seek medical help if you or your child experiences:

  • Breathing difficulties or shortness of breath

  • Persistent chest or abdominal pain

  • Sudden dizziness or confusion

  • A cough or fever that returns after improving

  • Signs of severe dehydration (e.g., dry mouth, sunken eyes, little or no urination)

  • Seizures or loss of consciousness

In children, red flags include:

  • Any fever in infants under 3 months old

  • High fever over 104°F in older children

  • Bluish skin or lips

  • Refusing to eat or drink

  • Not waking up or interacting as usual

  • Breathing very quickly or struggling to breathe

Questions for Your Healthcare Provider

If you are experiencing symptoms and need guidance, you may consider asking your provider:

  • What treatment options are best for my symptoms?

  • Am I at risk for flu-related complications?

  • How do I distinguish between flu and COVID-19?

  • Should I take antiviral medications?

  • How can I prevent spreading the virus to others?

Conclusion

Recognizing the symptoms of the flu early can help you take steps to recover faster and reduce the risk of spreading the illness. While many symptoms are familiar, such as fever, fatigue, and cough, it’s important to stay alert to severe signs that may indicate complications. Knowing when to rest, when to seek help, and how to care for yourself or a loved one is essential to navigating flu season safely and effectively.