What green snot means
Have you ever been told that green mucus/snot means you have a bacterial infection and need antibiotics? This is a common misconception.
Whoever told you that is wrong (and maybe you should share this article with them). This article discusses why mucus happens, what snot colors actually mean, and antibiotic use.
What is mucus?
Believe it or not, mucus is an integral part of our immune defense system. Remember, we are inhaling particles from the air ALL THE TIME. Smoke, dust, allergens and more are all present in our environments, and our body needs a way to constantly clear them. The best way to do this is to capture them in something sticky, and then send them back into the throat to be swallowed and removed. This is happening constantly - and on a typical day, you do not even notice it.
But when there is a sudden increase in exposure — for example, because a virus is attempting to enter the nasal passageways, the body kicks it up a notch. The inflammatory stimulus triggers a cascade that leads to a sudden increase in mucus as a protective maneuver. That increase in volume, and the change in consistency, are noticeable.
What is mucus made of?
Mucus is a watery substance that contains enzymes, white blood cells, and proteins/salts. It is made continuously (and in large volumes) by the epithelial cells that line our mucus membranes to help with lubrication - and while this article is focusing on the respiratory system, other similar linings in the body (such as the digestive and reproductive systems) also create mucus.
Is phlegm the same thing?
Kind of. Phlegm is made in the lower airways (the throat and lungs) rather than the upper airway (the nasal passages). It increases in volume as a response to inflammation.
Why does it change?
At baseline, mucus is usually thin and clear and limited in volume. When the body encounters an irritant (could be dust, blood, allergens or pathogens), proteins and white blood cells are sent to the mucus lining to help it out. These can change the consistency and color of the snot.
Sometimes the debris that the mucus collects can cause it to change.
Do the colors mean anything?
Yes, mucus color can be a helpful piece of information. But it is not a diagnostic piece of information - it is just one piece of a puzzle.
White or cloudy
Inflammation or irritation, dehydration, and sometimes dryness. This can signal just a thickening of the mucus or collection of debris.
Pink or red
Dried blood can change the color to pink or red, and this can happen for a number of reasons: nose-picking, trauma, frequent nose blowing (or frequent nose Frida use), infection, allergies or even dry air.
Yellow or green
The dark yellow or green color comes from myeloperoxidase, which is an enzyme that is released from white blood cells to help the immune system kill pathogens.
This immune response will happen regardless of whether a pathogen is a virus, fungus or bacteria.
Dead white cells can also accumulate to thicken the snot and change the color.
Brown or black
Old dried blood can make mucus look more brown.
Dirt, debris and cigarette smoke exposure can darken mucus as well.
Certain types of infection can cause dark mucus as well.
More about green snot
We do have research (PMID: 19242860) that indicates that green or yellow mucus is more likely to be caused by infection than white, clear or cloudy sputum. But because the green/yellow color comes from the white blood cells and enzymes, that snot color cannot tell us what type of infection is causing the symptoms.
Remember, antibiotics can only treat bacterial infections.
Antibiotics are wonderful medications when used correctly. They can save lives. But as with many other interventions, they also have disadvantages. They should be used, but only in the right circumstances. When used for a viral infection, they not only won’t make any difference but they also increase the risk of side effects and antibiotic resistance in the community.
In fact, some research even shows that people with yellow or green sputum are more likely to be prescribed antibiotics — but that those who were prescribed antibiotics did not get better more quickly than those who were not (PMID: 21406512).
So how can you tell what is going on?
Remember, mucus color is only one piece of the puzzle. Pay attention to it, but don’t freak out - especially because if the cause is viral, antibiotics will NOT help and may cause side effects.
Other factors that we use to figure out what is going on can include:
duration of nasal discharge
associated symptoms such as fever, cough, etc
exposures (and what is going around the community)
risk factors
In general, for symptoms that are worsening, not improved within 10-14 days, or associated with other red flags — OR if something is tickling your spidey sense — make sure you talk to your pediatrician. But don’t be surprised if your child doesn’t get antibiotics… they may not need them!
FAQ:
Q: Why does mucus cause a cough? And why is the cough worse at night?
A: Thick mucus with debris in it has to get out somehow. It can go forward (eg. when you blow your nose or use a nasal suction) or it can go backwards and get swallowed. For anyone who is laying down, the path of least resistance is towards the back of the throat.
When that mucus drips down the throat, it can trigger the cough reflex and lead to more coughing. In younger kids, who are not as adept at clearing their nasal passages of mucus, this is more likely. This is part of why I recommend a steamy shower and nasal suction before your child is put to bed. For other practical tips, click here.
Remember, raising the head of the bed is never recommended in young infants under age 1y because of the risk of closing off the airway.
Q: Does nasal irrigation help?
The data on this is interesting. I go through it in more detail here.
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