Key takeaways:
Flu-like symptoms include fever, chills, and body aches. But there are many conditions that can make you feel this way other than the flu.
Illnesses that can mimic the flu include the common cold, pneumonia, strep throat, and viruses like HIV and hepatitis C. And flu-like symptoms can come from other illnesses that aren’t even an infection.
For most people, fever and chills aren’t a cause for concern. But people with certain medical conditions should see a healthcare professional right away for any flu-like symptoms.
You’re probably familiar with that feeling when you know you’re getting sick. You are tired, your throat feels different, or maybe you feel colder than normal. And then you start to wonder exactly what’s going on. Is it the flu, COVID-19, or maybe just a cold?
It can be hard to tell the difference between these illnesses, especially when you first start to experience symptoms. But given there are a lot of different conditions that can start with flu-like symptoms, some people shouldn’t wait until things get worse.
What are symptoms of the flu?
There are a group of symptoms that are commonly associated with the flu. These symptoms include:
Fever
Chills and night sweats
Muscle aches
Sore throat, runny nose, or cough
Swollen lymph nodes in the neck
Nausea, vomiting, and diarrhea
Headache
Fatigue or malaise
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Which other illnesses can cause flu-like symptoms?
If you have flu-like symptoms, it doesn’t necessarily mean you have the flu. Many other illnesses can cause fever, body aches, chills, or headaches. When you feel like you’re coming down with the flu, here are some other illnesses that can feel the same way.
1. Common cold
The common cold is an upper respiratory infection that most people have had several times. A variety of different viruses can cause it — like rhinovirus or adenovirus.
Symptoms of a cold often include a sore throat, a runny or stuffy nose, and a cough. But it can also cause headache, body aches, and fever. Common cold symptoms tend to feel less intense than the flu. There isn’t a specific test for the common cold, and most treatments are just to help soothe the symptoms.
2. COVID-19
COVID and flu symptoms have a lot of overlap. Milder cases of COVID tend to feel more like the common cold and less severe than the flu. But moderate to severe cases can feel like the flu.
A few symptoms that are more likely with COVID include shortness of breath and loss of taste or smell. Whether you see a healthcare professional or take a test at home, you can be tested for both viruses at the same time.
3. Strep throat
Strep throat is caused by the bacteria group A Streptococcus. It’s more common in children and teenagers younger than 15 years. The main symptom is a very sore throat. But it can also cause fever, general fatigue, and achiness.
How long does the flu last? The worst of the symptoms usually pass within 7 days. But a full recovery can take longer than that.
Cold vs. flu: Learn about the differences in symptoms to help you know which one you have.
When should you go to the ER for a fever? Fevers are common. But depending on your age, there are some symptoms that shouldn’t wait to be treated.
A helpful clue is that when someone has a cough, too, this makes it unlikely to be strep throat. A swab from the back of the throat helps diagnose strep throat. Treatment includes antibiotics.
4. Pneumonia
Pneumonia is an infection of the lungs. It can be caused by either bacteria or viruses. The main symptoms of pneumonia include cough, fever, shortness of breath, and fatigue. And it’s important to note that the flu, COVID, and the common cold can also turn into pneumonia. But that’s not always the case. A chest X-ray can help figure out if you have pneumonia.
5. Mononucleosis
Mononucleosis — or “mono” — is usually caused by the Epstein-Barr virus (EBV). A sore throat is the hallmark symptom. But it typically comes with extreme tiredness and noticeably swollen lymph nodes in the neck.
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Most cases of mono occur in people younger than 30 years. It can be diagnosed with a swab or a blood test. There’s no specific treatment for mono.
6. Bronchitis
Bronchitis is an infection or inflammation of the lower parts of the airways. It usually starts with a virus that affects the lungs, but the cough can also last beyond the infection. This is because there can be ongoing inflammation after the actual infection has cleared.
Bronchitis tends to cause an irritating, dry cough. Treatment usually depends on your symptoms and other medical conditions. Some people benefit from inhalers and steroids.
7. RSV
Respiratory syncytial virus (RSV) is a common virus that causes flu-like symptoms. In adults, it often looks and feels like the common cold. But in young children — particularly those younger than 6 months — it can affect the lungs and cause dangerous breathing problems.
An infant with RSV tends to have rapid breathing and noticeable changes in their behavior. They may appear more tired than normal or have trouble feeding. Treatment may require oxygen and hospitalization for close monitoring.
8. Meningitis
Meningitis is an infection of the tissue that surrounds the brain and spinal cord. It usually causes headache, neck stiffness, and fever. The flu often causes fever and headache — but neck pain and neck stiffness aren’t common with the flu.
Meningitis is a potentially serious condition and needs medical evaluation right away. People with meningitis are usually hospitalized and treated with IV (intravenous) antibiotics.
9. HIV
In some cases, a new infection with HIV (or human immunodeficiency virus) can feel like the flu. Early symptoms of HIV range from fever, headache, and fatigue to swollen lymph glands, sore throat, and body aches. The symptoms may go away after a few weeks. If you have flu-like symptoms and think you may have been exposed to HIV, this is a good reason to talk with a healthcare professional about testing.
10. Botox
There’s evidence that some people experience flu-like symptoms after getting Botox injections. But the reports vary between different studies. One review found that between 1% and 20% of people report fever and fatigue after Botox treatment. Another study found the rate of flu-like illness to be about 16%.
11. Antidepressant withdrawal
When people abruptly stop their antidepressant medication, they can experience body aches, headache, and upset stomach. These symptoms can happen alongside mental health changes like anxiety or restlessness.
The name for this condition is antidepressant discontinuation syndrome. It’s likely caused by the sudden decrease in certain neurotransmitters, like serotonin and norepinephrine. It can happen with many different types of antidepressants. Symptoms typically last for 1 to 2 weeks. To avoid this, it’s best to work with a healthcare professional to slowly decrease your dose over time.
12. Hand, foot, and mouth disease
Hand, foot, and mouth disease (HFMD) is more common in children — but adults can get it, too. It’s an infection from a virus that causes painful mouth sores. Most adults who do get it report muscle aches and pains, and flu-like symptoms may be one of the earliest symptoms. The illness usually lasts about a week.
13. Hepatitis C
Hepatitis C is a viral infection that affects the liver. Unlike other infections, it is a chronic condition that can eventually lead to liver damage or even liver cancer. The virus is transmitted through blood. So someone can get the virus through unsterile needles.
Most people don’t have any symptoms of hepatitis until they develop liver damage. This can take 10 to 20 years. But some people develop flu-like symptoms at the time of initial infection. If you’ve never been tested for hepatitis C, talk with a healthcare professional. Everyone should get tested at least once in their lifetime. And with treatment, it’s curable.
14. Carbon monoxide poisoning
Carbon monoxide is an odorless gas produced by burning different types of fuel — from wood to natural gas. So carbon monoxide levels can quickly rise in homes, particularly in the colder months when stoves are burning and windows are closed.
When people first start to get sick from carbon monoxide, the symptoms might feel like the flu. But this can quickly progress to confusion, loss of consciousness, even death. If you’re concerned about carbon monoxide in your home, get everyone outside and call for emergency help.
When should you get medical attention for flu-like symptoms?
People who have a higher risk of severe infection should see a healthcare professional for any flu-like symptoms. These include:
Very young children
Adults older than 65 years
People who are pregnant or immediately postpartum
People with neurologic disorders, like a history of seizures
People with serious lung or heart conditions, like chronic obstructive pulmonary disease (COPD) or heart failure
People with a weakened immune system
You should also get medical attention right away if you have any of the following:
Severe difficulty breathing or fast breathing
Persistent vomiting
Inability to stay hydrated
Extreme muscle tenderness
Dizziness or feeling like you’re going to pass out
Pain or pressure in the chest or belly
No improvement in symptoms after 3 to 5 days
Symptoms that start to improve and then get worse again
How can you tell if you have the flu, COVID, or something else?
The only way you can know for sure what’s causing your flu symptoms is to get tested. The easiest and most efficient way is to see a healthcare professional. They can perform many of these tests at the same time. For example, nose and throat swabs can test for:
COVID
Flu
RSV
Strep throat
Mono
Testing for serious flu-like symptoms
If your test results are all normal, it could mean you just have the common cold. But if your symptoms are more serious, your healthcare team may recommend additional testing to look for other causes. These tests may include:
A chest X-ray to look for pneumonia
Blood tests to look for signs of infection, like blood counts or a blood culture
Blood tests for HIV, or other more rare infections
A lumbar puncture for meningitis
For most people, this extra testing won’t be necessary. But when in doubt, it’s always a good idea to ask a healthcare professional’s opinion.
Can you have the flu without a fever?
Yes, you can have the flu without a fever. In fact, one study found similar rates of fever across adults who had the flu, COVID, RSV, or a common cold. And only about 1 in 3 adults with the flu had a fever.
Adults are less likely than children to have a fever with the flu. You’re also less likely to have a fever with the flu if your immune system is weaker. This includes older adults, and people with conditions or medications that affect immune system function.
Frequently asked questions
Yes, certain cancers can cause flu-like symptoms. One cancer that tends to do this is lymphoma — specifically B cell lymphoma (also called non-Hodgkin lymphoma). But many different types of cancers can cause symptoms like fever, fatigue, and swollen lymph nodes. But while cancer can cause flu-like symptoms, other conditions are more common and more likely.
Yes, it’s possible to have strep and flu at the same time. Although this isn’t common, it’s more likely for people who have a weaker immune system. Both of these conditions can be diagnosed with a simple swab test. So if you think you have both strep and flu, see a healthcare professional for testing.
Stress can take a big toll on your physical health. And it can lead to symptoms that may feel like the flu, especially fatigue, headache, change in appetite, change in bowel habits, and unexplained body aches. There are even reports of stress causing a fever.
Yes, the flu can make you dizzy. This is a common symptom that can accompany any illness that causes a fever or headache. It’s also common to experience dizziness when you get dehydrated, which is common with the flu. The dehydration can be due to vomiting or diarrhea, or simply from the presence of a fever and decreased fluid intake.
Yes, certain cancers can cause flu-like symptoms. One cancer that tends to do this is lymphoma — specifically B cell lymphoma (also called non-Hodgkin lymphoma). But many different types of cancers can cause symptoms like fever, fatigue, and swollen lymph nodes. But while cancer can cause flu-like symptoms, other conditions are more common and more likely.
Yes, it’s possible to have strep and flu at the same time. Although this isn’t common, it’s more likely for people who have a weaker immune system. Both of these conditions can be diagnosed with a simple swab test. So if you think you have both strep and flu, see a healthcare professional for testing.
Stress can take a big toll on your physical health. And it can lead to symptoms that may feel like the flu, especially fatigue, headache, change in appetite, change in bowel habits, and unexplained body aches. There are even reports of stress causing a fever.
Yes, the flu can make you dizzy. This is a common symptom that can accompany any illness that causes a fever or headache. It’s also common to experience dizziness when you get dehydrated, which is common with the flu. The dehydration can be due to vomiting or diarrhea, or simply from the presence of a fever and decreased fluid intake.
The bottom line
Flu-like symptoms are common, especially in the fall and winter. And when they start, it can be difficult to know if you have the flu or another illness like COVID, a common cold, or strep throat. If you think you might have the flu but aren’t sure, see a healthcare professional for an exam. They can figure out if you need more testing or treatment. This is especially important if you’re in one of the groups at higher risk for many different causes of flu-like symptoms.
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References
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Centers for Disease Control and Prevention. (n.d.). Respiratory syncytial virus infection (RSV).
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Chughtai, A. A., et al. (2016). The presence of fever in adults with influenza and other viral respiratory infections. Epidemiology and Infection.
New York State Department of Health. (2021). COVID-19, influenza (flu), and HIV: Similarities and differences.
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Silvennoinen, H., et al. (2009). Clinical presentation of influenza in unselected children treated as outpatients. The Pediatric Infectious Disease Journal.
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