Is It COVID, Flu or Allergies? How to Detect What’s Making You Sick

You’re bound to encounter some type of illness this winter, but how do you tell which virus you have? And how do you know if what you’re experiencing is just allergies? It’s important to figure it out, since viruses that cause the flu, COVID and RSV are all contagious, while allergies aren’t and don’t require the same social-distancing precautions. (And yes, allergies are still common during the winter.)

It may be too soon to tell how severe the flu will be this year, since most flu activity typically peaks between December and February, according to the US Centers for Disease Control and Prevention. However, an increase in COVID and flu cases can be expected around the holidays, when more people are gathering indoors. 

Besides flu and COVID, specific groups worry about RSV. The CDC recommends that all adults age 75 and older and adults ages 60-74 who are at increased risk of severe RSV get an RSV vaccine. For pregnant people, vaccines are available, along with monoclonal antibody products, to protect infants and young children from severe RSV. What’s more, the CDC recently lowered the vaccine recommendation to age 50 for the pneumococcal vaccine, which guards you against one common cause of pneumonia.  

Here’s what to know about flu and COVID symptoms, as well as some clues to look for regarding whether you’re sick with a virus rather than allergies (or vice versa). If you’d like to learn more, here’s our guide to which vaccines adults 50 and older should consider, our explainer on how to order more free COVID tests, and our rundown of what to know about at-home tests that detect COVID and flu.

Flu vs. COVID symptoms — is there a difference? 

Not really, according to Dr. Amesh Adalja, an expert in infectious diseases and a senior scholar with the Johns Hopkins Center for Health Security, who spoke with CNET via email in late 2023.

“There is no real way to distinguish COVID-19 from influenza based on clinical symptoms because they overlap so much,” he said. Common COVID and flu symptoms include sore throat, fever, fatigue, muscle aches, cough and more. The big COVID symptom, loss of taste and smell, has become much less common than during the peak of the pandemic. 

There may be a slight difference in how soon your symptoms show up after getting infected with the flu vs. COVID, though, according to the CDC. Flu symptoms may appear one to four days post-infection, vs. two to five post-COVID infection, and some people may take up to two weeks to show COVID symptoms, according to the CDC. But because the average window to develop symptoms is similar for both viruses, you likely won’t be able to tell based on this criteria either. 

Both COVID and the flu cause the most severe illness and lead to complications in the same populations: adults in their 60s and up and younger people with certain medical conditions. If you’re planning on spending time with someone at high risk of any virus, it’s especially important that you err on the side of caution and wait until you’re no longer sick to see them face-to-face. 

If you are at higher risk, you should speak with your doctor about getting a real diagnosis for the appropriate treatment. Flu has a different treatment than COVID-19, but antivirals for either should be started immediately.  

What about RSV?

RSV is a common virus that causes only mild symptoms in most adults, such as a runny nose, decreased appetite and fever. But in older adults and young babies, it can cause severe symptoms, like pneumonia or trouble breathing.

Vaccines for RSV are now available to older adults and to pregnant people, to protect newborns once they’re born. Some infants may also receive a monoclonal antibody as protection against RSV. 

Quick tips to help check whether it’s allergies or a virus 

“It’s very common that people who have allergies, they think they’re having a series of viral infections,” Dr. Geoff Rutledge, chief medical officer at HealthTap, told CNET during spring 2022. And on the other end, some people have reported COVID-19 symptoms from newer versions of the virus that are typically linked to allergies, including pink eye. That can make it even trickier to know what you have.

However, Rutledge said some symptoms and clues are “very suggestive” that you’re experiencing a virus rather than seasonal allergies or vice versa.

If you have a fever, it’s not allergies

While “fever” is in the name, hay fever does not actually cause a fever, according to the American College of Allergy, Asthma and Immunology. However, if you have a sinus infection or other bacterial infection, that may cause a fever and can be caused “sometimes secondarily” by allergies, according to Rutledge. 

If you’re really itchy, it might be allergies

“Allergies typically cause itching of either the eyes, nose or top of mouth, which is not usually common in viral infections,” Dr. Jennifer Bourgeois, pharmacy expert at SingleCare, told CNET in an email during spring 2022. It’s important to note that while it’s hard to pin symptoms down to specific variants of COVID-19, there have been some reports of conjunctivitis or pink eye connected with the COVID virus. Viruses and bacteria can also cause pink eye, which in turn can cause itching around the eye.

According to the Cleveland Clinic, other symptoms of allergic rhinitis besides itching include congestion; sneezing; headaches and sinus pain; dark circles under the eyes; increased mucus; postnasal drip (mucus draining down the back of your throat); trouble breathing; and fatigue or generally feeling bad. 

Take an at-home COVID test 

This one’s pretty simple, but the best way to find out whether you have COVID-19 is by taking an at-home test, or a more accurate lab test at a doctor’s office. This might be especially important if you plan on being around a person who’s older or otherwise at higher risk of serious illness from COVID-19. 

The FDA recently authorized a new at-home test for both COVID and flu, the first one outside of pandemic-era marketing rules, and it’s expected to be available around Thanksgiving time. There are other at-home tests on the market, such as this one, that can distinguish between COVID and flu and that have emergency use authorization. 

In September, the USPS started offering four free at-home COVID test kits to US households. 

Take the antihistamine test 

For people who experience seasonal allergies but aren’t entirely sure if that congested feeling is from the same cold your friend had or the familiar allergies that usually kick in this time of year, Rutledge suggested what he calls a “therapeutic trial” of taking an over-the-counter antihistamine to see if that clears up your symptoms. 

“There are specific treatments that only work for allergies,” he said, and antihistamines are one of them. Histamine is what your body releases when you have an allergy and your immune system is activated. Antihistamines work by blocking the effects of histamine and helping many allergy symptoms. On that note, if you have sinus pain or sneezing and your symptoms improve after you take an antihistamine, it might be safe to say you have allergies.

COVID, flu and RSV treatments 

Antiviral medications like Paxlovid may be prescribed for older adults and younger people who have a higher risk of getting severe illness from COVID-19. For Paxlovid to work, you need to start the medication within the first few days of your symptoms appearing. 

Flu treatments are also available for people at higher risk. Like COVID, it’s important for people at risk to start antiviral medication for the flu as soon as possible. 

What are some effective allergy treatments?

In terms of allergies, what kind of medication you need depends on which symptoms you have. 

“Each medication is designed to treat specific symptoms, so it’s important to find the correct over-the-counter medicine in order to manage and relieve your symptoms,” Bourgeois said. For example, antihistamines like Claritin or Zyrtec are standard allergy medications, but you could also find relief from a decongestant. 

In a pinch, fever-reducing medications like ibuprofen might also work for allergies because they have anti-inflammatory properties, Bourgeois said.

You might even try stopping allergy symptoms before they start with a steroid nasal spray, according to Bourgeois. They do the work before you’re exposed to the allergens in the air.

“It is best to begin the steroid nasal spray a couple of weeks before the allergy season that triggers your symptoms and continue throughout the duration of the season, as it’s typically not required to use the steroid nasal spray all year long,” she said.

If you choose to do a nasal rinse after symptoms and mucus sets in, Bourgeois referred to the CDC’s guide for safely carrying it out with sterile material. 

Many people will manage allergy symptoms with help from their primary doctor or the right medication, Rutledge said, and they won’t need further medical help. But if you’re still not getting relief from your symptoms, and you’ve done some detective work into what’s causing your allergies, then you might be a good candidate for in-clinic allergy testing or a follow-up appointment with a specialist to get to the source, according to Rutledge.