Is It the Flu? 8 Most Common Flu Symptoms in Adults

You’re probably aware of the many different respiratory illnesses floating around in wintertime, like the common cold, COVID-19, and flu. These illnesses often have overlapping symptoms. So when you start to feel sick, it’s common to wonder what your symptoms might mean.

In adults, flu symptoms tend to appear suddenly. They usually start within a couple of days of being infected and peak around day 3 or 4 of illness. Most adults feel sick for about a week, although symptoms can sometimes last longer.

Here, we’ll review the most common flu symptoms in adults and explain when you should consider getting medical attention for them.

Body and muscle aches

The most common flu symptom in adults is myalgia, or muscle aches. This can affect almost any muscle in your body, even your eye muscles. Research suggests that almost all adults with the flu will experience body aches, and they can be miserable. Some people describe it as feeling like they were “hit by a train.”

Cough

A cough is also a very common flu symptom in adults. But coughs are common in many other respiratory illnesses as well, so they aren’t specific to the flu. That said, research suggests that having both a fever and cough within the first 48 hours of an illness is a pretty clear signal of the flu.

Unfortunately, this cough can linger for a week or two, even after your other symptoms have gone away.

Headache

Headaches from the flu usually occur early in the illness and are very common. They can be caused by sinus pressure, dehydration, or your body’s response to the virus. How long the headache lasts can depend on how long your congestion lasts.

A flu headache typically feels like aching or throbbing pain all over your head. The flu can also trigger migraine headaches in people who are susceptible to them. 

Nasal congestion / runny nose

Nasal congestion and runny nose are among the most common flu symptoms in adults. Over 90% of people with the flu have one or both. But like a cough, these symptoms aren’t specific to the flu. Runny nose and congestion can last for the entire week of your flu symptoms.

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Fatigue / weakness

The extreme tiredness and weakness that can come with the flu are very common. They affect up to 94% of adults with the flu. When combined with other symptoms, like muscle aches, this weakness tends to make the flu feel worse than other respiratory illnesses. It can make it difficult to perform daily activities, making you more likely to stay in bed or on the couch.

Fever

A fever, defined as a temperature over 100.4°F (38°C), isn’t as common as some of the other symptoms listed above. In other words, it’s possible to have the flu without a fever. This is especially true for older adults.

For those who do get a fever, it usually appears early in a flu illness and lasts for a few days.

Sore throat

A sore throat affects about 84% of adults with the flu. It can make swallowing painful, which can make it difficult to stay hydrated. A sore throat may also make your voice sound hoarse.

If you have a sore throat without other flu symptoms, it could be caused by something else, like strep throat.

Diarrhea

Although the flu is primarily a respiratory infection, it can also cause gastrointestinal problems like diarrhea. This isn’t a common flu symptom in adults. Kids are more likely to get diarrhea when they have the flu. But adults can develop flu-related diarrhea. It can last between 2 and 5 days. 

How do you treat adult flu?

Most people recover from the flu with home remedies and over-the-counter (OTC) medications, like:

• Rest

• Drinking fluids

• Nasal saline rinses

• Fever reducers (like ibuprofen or acetaminophen)

Some people may also benefit from prescription antiviral medications, like Tamiflu. These medications work best when taken within the first 2 days of flu symptoms. Antiviral medications take 1 to 2 days to kick in, but they can shorten the duration of illness.

Be sure to stay home while you’re sick to avoid spreading the flu to others.

When should you get medical care for flu symptoms?

You should seek medical care right away if you have flu symptoms and any of the following:

• Chest pain

• Difficulty breathing

• Severe weakness or fatigue

• Ongoing dizziness or lightheadedness

• Not urinating (due to dehydration)

• Symptoms that don’t improve or get worse after 1-2 weeks

These could be signs and symptoms of a severe illness. Or they could mean something else is causing your symptoms. You may also be developing a complication or an additional medical issue from the flu infection. Examples of flu complications include bronchitis and pneumonia.

Who is at higher risk for flu complications?

Some adults are at higher risk for flu-related complications, including those who:

• Are over the age of 65 

• Have chronic lung disease like asthma or chronic obstructive pulmonary disease (COPD)

• Have heart, kidney, or liver disease

• Have diabetes

• Have a weakened immune system

• Are pregnant

If you’re at high risk for flu complications, it’s best to get medical care earlier in your illness. You can also consider seeing a healthcare professional to get tested for the flu. Testing can provide immediate results and help you start antiviral medication right away if needed.

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Written by:

Mandy Armitage, MD

Mandy Armitage, MD, has combined clinical medicine with her passion for education and content development for many years. She served as medical director for the health technology companies HealthLoop (now Get Well) and Doximity.

Edited by:

Katie E. Golden, MD

Katie E. Golden, MD, is a board-certified emergency medicine physician and a medical editor at GoodRx.

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