When mucus is dripping out of your nose, don’t wipe it into a tissue — use it instead to find out whether you have a cold or the flu.

Scientists have found a way to measure protein in that gooey discharge that will tell you the difference between influenza and human rhinovirus, the cause of the common cold. According to a study in EBioMedicine, the diagnostic tool essentially measures how the body is responding to the infection and could be used to quickly screen for illness, as well as help doctors avoid using antibiotics when they are not needed. It may also aid “more rapid implementation of … public health strategies.”

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“Although upper respiratory infections are among the most common reasons people visit the doctor in the U.S., health care providers lack tools to distinguish between a bacterial infection that might warrant antibiotics and a viral infection that would instead call for symptom relief,” Duke University Medical Center said in a statement. “Widespread use of antibiotics for upper respiratory infections doesn’t benefit patients with viral illness and can contribute to antibiotic-resistant superbugs,” so it’s important not to use them when they are not necessary.

Measuring proteins in the mucus is more precise than simply looking out for symptoms of the flu or a cold, which can appear the same to an untrained eye. The flu is more intense and lasts longer than a cold, and often comes with a fever, chills, a cough, sore throat, a stuffed or runny nose, body and headaches and fatigue. But its most serious danger is in complications like asthma attacks, pneumonia and swelling in the heart or brain. Colds are more focused on nasal symptoms.

Another cause of symptoms could be something that isn’t an infection at all — it could be winter allergies to dust mites, animal dander, mold or other irritants that are constantly re-circulating through your home when all the windows are closed.

According to the EBioMedicine study, apart from better diagnosing illness, the protein-measuring tool tells experts more about how the body responds to infections and disease, which is information that could lead to new treatments. Additionally, it “reinforces the important concept that host response to infection … serves as a potential basis for diagnostic testing,” rather than just checking the blood for a pathogen, for example.

“Every day, people are taking time off from work, going to emergency rooms, urgent care or their primary care doctors with symptoms of an upper respiratory infection,” researcher Dr. Geoffrey S. Ginsburg, director of the Duke Center for Applied Genomics & Precision Medicine, said in the Duke statement. “Looking for these proteins could be a relatively easy and inexpensive way of learning if a person has a viral infection, and if not, whether the use of antibiotics is appropriate.”

Source: Ginsburg GS, Woods CW, Burke TW, et al. Nasopharyngeal Protein Biomarkers of Acute Respiratory Virus Infection. EBioMedicine. 2017.

See also:

Follow These Good Habits to Stop Spreading Your Sickness

Here’s Why You’re Always Cold