If you’ve ever peeked into your tissue after blowing your nose and glimpsed yellow mucus, you may have wondered what your body was trying to tell you. Fear not! Mucus the color of lemonade is a sign that your body is doing what it’s supposed to do when faced with outside intruders.
Mucus is critical for the health of your respiratory and immune systems.
This slimy stuff helps to warm and humidify the air you breathe, Anthony Del Signore, M.D., assistant professor of otolaryngology and director of rhinology and endoscopic skull base surgery at Mount Sinai Beth Israel, tells SELF. This is important because breathing air that’s too cold and dry can aggravate your airways, which is why it can burn like hell to breathe outside in wintertime. So, even though mucus is kind of gross, it contributes a fair amount to your physical comfort.
Mucus is meant to keep you comfortable in another way, too: as a vigilant guard on the frontlines of your body’s biological defense system, Michael Benninger, M.D., chairman of the Cleveland Clinic Head and Neck Institute, tells SELF. Mucus traps foreign invaders that could make you ill, including viruses, bacteria, and allergens. Ideally, little hair-like projections called cilia then shuffle those invaders to the front of your nose so you sneeze them out, meaning they can’t enter your lungs and make you sick. (This dirty mucus can also slip down your throat, but if invaders get to your lungs, you might cough to clear them out.)
Your mucus usually turns yellow when your body is fighting an infection.
When your mucus traps potential illness-causing debris, like pathogens that cause the common cold or flu, your immune system sends inflammatory cells such as white blood cells to the area to help destroy the invaders, Dr. Benninger explains. It’s this inflammatory response—not the agents of infection themselves—that causes the signature shift in mucus hue, Dr. Benninger says.
One of the first responders to microbial invaders is a type of white blood cell called a neutrophil. Neutrophils are full of myloperoxidase (MPO), an enzyme that contains green-colored heme, or iron. When super-concentrated, these green neutrophils can make your mucus appear straight-up verdant. But when less concentrated, the mucus appears pale green—which, depending on how your eyes work, might look yellow to you instead.
You may also notice that your mucus is a deeper shade of yellow (or looks like it has gone from yellow to green) after several days of being sick, not blowing your nose for a while, or when you wake up in the morning. When mucus sits around in your nasal passages for prolonged periods, these inflammatory cells can build up and tint your mucus more intensely, Dr. Benninger explains. “The less you clear it out, the more it becomes discolored,” he says.
So, when you’ve got yellow mucus, you should blow your nose often to clear out any trapped debris and keep things moving.
Yellow mucus isn't necessarily a sign you need to see a doctor.
What really matters is your accompanying symptoms and how long they stick around, Dr. Benninger says. While you know your body better than anyone and should take a trip to the doctor if you’re feeling unusually horrible, it’s good to know that some of the most common illnesses involving yellow mucus will typically clear up on their own without medication.
For example, the common cold usually lasts seven to 10 days, according to the Mayo Clinic. A viral sinus infection typically begins to clear up after five to seven days, while a bacterial sinus infection may last seven to 10 days, hang around for longer than that, or even worsen around a week in before eventually fading, according to the Cleveland Clinic.
In the meantime, you can use over-the-counter meds and at-home care to manage symptoms of these kinds of illnesses. Methods include anti-inflammatories for pain and fever, nasal irrigation, and decongestants if you have an especially clogged nose, Dr. Benninger says. (You shouldn’t use decongestants that constrict your nasal blood vessels for more than three days, though, or they can cause rebound congestion. Learn more about that here.)
If you still feel like something stuck on the bottom of a shoe after around a week of being sick, you might want to check in with a doctor. It’s possible that you could need something like antibiotics to clear up a bacterial sinus infection. No matter what’s going on, your doctor can help determine the cause of your yellow mucus and get your snot crystal clear again.