Every year around flu season our offices are packed with patients with all kinds of coughs, colds, and sniffles. Inevitably, the conversation will include a description of mucus.  “I felt bad 3 days ago, then started seeing yellow mucus, but today it is green so I know I need an antibiotic.”

In reality, the color of mucus is rarely used as an indication by itself for the presence of an infection or not. Patients with clear mucus can actually have severe infections, and patients with green bloody mucus can be fine. Doctors look at the big picture and things like fever, wheezing, inflammation, cough, and vital signs to more accurately figure out what is going on.

Clear mucus is normal mucus. Composed mostly of water, clear nasal discharge is produced at rates up to 1.5 liters daily, and commonly runs down the back of the throat and dissolves in the stomach. Allergies and congestion can cause more of it to be produced, and the absence of color generally means there is no infection present.

Common viral nasal infections (like the common cold) can create a more dense, thick white mucus. This is essentially a healthy clear version that is dehydrated. The fat from dairy products can also generate a thick, white mucus in some people.

Mucus that is yellow signifies a greater presence of white blood cells that have rushed in to fight an infection. A clear or white mucus mixed with dead white blood cells, proteins and antibodies will be yellow in appearance. This is usually caused by allergies, congestion, and infection – often viral – but possibly bacterial. It is the presence or absence of other symptoms that help doctors determine the source.

Green is usually the next step and the color that primary care physicians hear about the most. Commonly misconstrued as the hallmark sign of a bacterial infection, it is simply the sign of your body’s immune system really fighting off any type of infection – usually something viral. As with yellow mucus, green mucus is thick with dead white blood cells, proteins, and antibodies. Viral infections can be miserable and last for upwards of 10-14 days (without the need for ABx), so other symptoms and past medical history are important. For most people, green mucus by itself is not a big deal, especially if it has only been present for 24 hours or less.

Pink, red, or brown mucus is concerning for small amounts of blood, but most of the time the source of bleeding is small scratches from rubbing, sneezing, wiping too often, or dry and irritated mucous membranes inside the nose. The nose is a very vascular structure, and most allergy medicines “dry up” mucous membranes – so nosebleeds during allergy season are very common.

All of that being said, if your mucus is clear, yellow, green, or neon pink – it is never a bad idea to go get it checked out if you are feeling poorly. Keep eating well, staying hydrated, washing your hands, and getting plenty of rest as we continue to power through this year’s flu season!