You—or your child—have body aches, fever, and cough. Is it RSV, COVID, the flu, a common cold, or something else? And does it even matter anymore?

Unfortunately, it’s impossible to definitively tell the conditions apart without testing—even by cough, experts tell Fortune. But the answer will still matter, if your condition is severe and a treatment plan is needed.

What is the difference between COVID, RSV, the flu, and a common cold?

COVID, RSV, the flu, and common colds all come from contagious respiratory viruses. What’s more, additional flu-like viruses circulate as well, muddying matters.

Now in the fifth year of the pandemic, we’re all too familiar with COVID, especially given this winter’s JN.1 surge—the second largest wave the U.S. has seen so far. For the most part, symptoms have remained the same. Though there’s talk of the variant possibly leading to more severe disease and additional GI symptoms like diarrhea, nothing has been confirmed.

While COVID hospitalizations and deaths are up this winter, JN.1 itself may not be to blame. Rather, the rise in severe illness could be due to waning population immunity. The majority of Americans haven’t received the latest COVID booster, according to the U.S. Centers for Disease Control and Prevention. Whether it’s from illness or vaccination, antibody immunity to COVID only lasts three to six months, on average.

RSV, or respiratory syncytial virus infection, is a common illness that usually presents as a mild cold. Almost everyone has been infected with it by age 2, according to the CDC. But RSV isn’t mild for everyone. The virus hospitalizes tens of thousands of infants, young children, and elderly adults each year in the U.S. And it kills between 6,000 and 10,000 elderly adults in the U.S. annually, according to the national public health agency.

Last year, levels of RSV, COVID, and flu rose early and dramatically at the same time—part of what some public health officials called a “tripledemic” that coincided with the lifting of pandemic restrictions. This year, combined levels of respiratory illnesses rose later than they did last year. While they haven’t peaked yet, the current respiratory season is, so far, more mild than last. While levels of RSV and flu may be on the brink of cresting, they haven’t quite yet. Some good news: Levels of COVID have peaked for now, though the downward trend could certainly reverse at any moment.

While there are distinct differences between all four illnesses, they can present differently, depending on the patient. That’s why it’s impossible to tell the them apart by symptoms alone.

Are RSV, COVID, flu, and cold coughs different?

Unfortunately, both COVID and RSV can result in different types of cough, including dry, wet, wheezing, and the like, Dr. Dan Olson, associate professor of infectious diseases and epidemiology in the Colorado School of Public Health at the CU Anschutz Medical Campus, tells Fortune.

While children with a lower respiratory infection like RSV tend to wheeze, such noises may only be apparent to medical providers. The typical nonclinician parent usually won’t be able to detect it, Dr. Ishminder Kaur, an assistant professor of pediatric infectious diseases at UCLA Health, tells Fortune.

The flu usually leads to a dry cough, and a cold tends to cause a slight cough. However, you can have any of the four conditions without cough.

How do RSV, COVID, cold, and flu symptoms differ?

All conditions can lead to aches, difficulty breathing, fatigue, fever, loss of taste or smell, cough, sore throat, and wheezing. Difficulty breathing is more common in COVID, while wheezing is more common in RSV, according to the National Foundation for Infectious Diseases (NFID).

In general, however, there are no distinctive clinical characteristics that can conclusively distinguish the flu from COVID from RSV from a cold without testing, experts say. But there are some potential tells:

• Symptoms like headache, loss of taste or smell, or sore throat “can point away from RSV,” Dr. Ali Alhassani, head of clinical at Summer Health, tells Fortune.

• GI symptoms like nausea, vomiting, and diarrhea can occur in COVID, sometimes in absence of respiratory symptoms, Dr. Ishminder Kaur, an assistant professor of pediatric infectious diseases at UCLA Health, tells Fortune. Such symptoms usually don’t occur with RSV.

• Children with COVID usually have a fever, while children with RSV may not, she adds.

• Sore throat is more common with COVID, according to Kaur.

• Those with COVID sometimes get conjunctivitis (redness of the eyes) and skin rashes—symptoms not generally seen in RSV, she says.

• Body aches, fatigue, and fever are most common in the flu and COVID, according to the NFID.

Does it matter which one I have?

With society functioning as if the COVID-19 pandemic is over, does it even matter any more which illness you, or a loved one, has?

Yes, experts say. That’s because if treatment is required, a precise plan will need to be formulated. Antivirals like Paxlovid are available to children and adults with COVID ages 12 and older. While no specific treatment is available for RSV, supportive care at a hospital may be needed in either case. (And by the way, it’s possible to have two or more viruses at the same time.) Antivirals like Tamiflu are available to high-risk patients.

Can I test for COVID, flu, RSV, or cold at home?

At-home testing kits are available for COVID, of course. But while at-home collection kits exist for RSV and the flu, none will give you results in home. A trip to your doctor or urgent care will be necessary. (Your doctor can run tests to see if you have a virus that causes common colds. But such a test won’t be necessary unless you have severe symptoms.)

When should I worry about my sick child?

Parents should seek care for their children if they witness any of the following, experts tell Fortune:

• Fast breathing or difficulty breathing, which may look like chest wall retractions and/or nasal flaring

• Head bobbing or pauses in breathing in young infants

• Lethargy

• Dehydration (reduced urine output)

But if your child’s symptoms aren’t resolving on their own after a few days, “it might be time to consult with a pediatrician,” Alhassani advises.