The difference between the flu, a cold and allergies

Is your runny nose due to a cold, allergies or the flu?. Getty Images

If you have a runny nose, a stuffy head, and generally feel under the weather, how do you know whether it’s allergies making you feel miserable, a cold, or the more serious flu virus?

With the current flu season showing no signs of slowing down anytime soon it is important to know to treat accordingly, and if you do have a virus to avoid passing it to someone else.

Isabel Valdez, a physician assistant and instructor of family and community medicine at Baylor College of Medicine, gives her expert tips on how to tell what is going on.

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– A big indicator that you have the flu is when symptoms such as body aches, fevers, chills, nausea, an upset stomach or night sweats suddenly start occurring, Valdez said.
– A high fever, above 101 degrees, is also a sign that it is the flu and not a cold.
– The flu should also last about one to two weeks, with Valdez adding that “if your runny nose or congestion is lingering, it could be allergies.”

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– For those who haven’t had the flu yet, Valdez also stressed the importance of getting the flu shot to help prevent catching the virus. “The flu shot is there to protect you. You want to get the flu shot so that you can launch an immune response to the real infection if you are exposed to the flu,” she said. “Also, if you do contract influenza, it will hopefully help you get over the illness quicker.”

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-The big difference between cold and flu is that a cold often does not come with a high fever and/or body aches, explained Valdez. A cold will often come with a low not high fever, between 99 and 100 degrees, which does not last long.
-A cold typically follows a pattern which starts with a sore throat at the beginning, then congestion for a few days, and then as the congestion starts to clear a cough can develop which also lasts for a few days.

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-Don’t rely on mucus colour to tell you if you need medication, with Valdez commenting that, “Everybody thinks that if they have green mucus, they need an antibiotic but that’s not necessarily the case. A lot of the time, you can start the day with yellow-green mucus when you have a virus but as long as that mucus gets lighter in colour and thinner in consistency as the day progresses then you don’t need antibiotics.”


-Clear, runny mucus, as opposed to yellow or green, tends to indicate an allergy not a virus.
-Also look out for a stuffy nose, scratchy throat or feeling pressure around the eyes with mild allergies, which can be brought on by changes in the weather. These symptoms can be treated with over-the-counter allergy medications, antihistamines and nasal sprays.

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-Exposure to excessive heat, for example by cranking up the heating in cold weather, can also cause irritations in the nose, mouth, and throat as they dry out due to lack of moisture. “Sometimes if people dry out their noses too much, this can lead to them having little nose bleeds or when they blow their nose they will notice blood in the mucus and, again, this is because the mucosa inside their nostrils gets so dry and fragile from the heat that little blood vessels will pop,” Valdez said. “Usually if this happens, I recommend that patients start to use a nasal saline spray to moisturize their nostrils.”


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