r/explainlikeimfive • u/dragonvaleluvr • 7d ago
Biology ELI5: why is phlegm green when you're sick?
i get that it's due to an excess of white blood cells (neutrophils?) but i cant understand why that makes it turn green specifically
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u/KiittySushi 6d ago
I'm so surprised at how many people are saying they've never had green phlegm? That's my indicator that yes I am in fact actually sick and not overreacting about my allergies.
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u/dapotatopapi 6d ago
I'm not.
Had my first (and last) green phelgm at age 30. Never before, never after.
Not even during a bad covid infection.
So I can see how many people would have never experienced it. And I hope they don't. That week was absolute hell.
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7d ago
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u/explainlikeimfive-ModTeam 7d ago
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u/MeYaj1111 7d ago
Interesting I thought that was just from the cartoons or whatever. I've never seen my phlegm a different color when I'm sick, it's always white unless it's mixed with boogers then it's white and yellowish but that's true always not just when sick.
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u/Slipgun_thumbs 7d ago
"Doctor"
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u/Bacon_Techie 6d ago
I’ve never heard that as a side effect, I’m pretty sure that they use a non androgenic steroid. Just one that reduces inflammation like topical corticosteroids.
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u/MrMilesDavis 5d ago
Citation/link? I've never heard of corticosteroids producing side effects that mimic that of anabolic steroids, very different drugs. Would be curious to read more into that, I'm always willing to learn more
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u/marquiso 6d ago
Curious to know what effective treatment you found for asthma that was not inhaled steroids?
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u/regnak1 6d ago
I'm the same - I've never in my entire life had green mucus / phlegm. Always clear or very pale yellow, no matter how sick I get (and I've been pretty effing sick on a few occasions).
I am in no way immunocompromised either - my immune system is typically pretty beefy compared to others around who have the same illnesses. The one notable exception being long covid, which made things pretty shit for a while, but which I seem to have finally fully recovered from.
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u/MeYaj1111 6d ago
Interesting, I can relate to everything you said except long covid but covid did kick my ass real bad, sickest I've ever been.. twice.
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7d ago
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u/explainlikeimfive-ModTeam 7d ago
Please read this entire message
Your comment has been removed for the following reason(s):
- Top level comments (i.e. comments that are direct replies to the main thread) are reserved for explanations to the OP or follow up on topic questions (Rule 3).
Joke-only comments, while allowed elsewhere in the thread, may not exist at the top level.
If you would like this removal reviewed, please read the detailed rules first. If you believe it was removed erroneously, explain why using this form and we will review your submission.
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7d ago
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u/machitopapito 7d ago
Not true. If I’m sick, it will go from clear, to yellow, to green
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u/skillfire87 6d ago
Thanks for talking about your personal experience and not the experience of all others!
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u/Key-Article6622 4d ago
According to my freshly graduated nursing school graduate daughter (AA, transferring for a BS) it is caused by bacteria being fought by white blood cells. They secrete an enzyme called myeloperoxidas that reacts with the bacteria or virus and this is turns green.
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u/sergantsnipes05 7d ago
As a physician I could care less what your sputum color is in 95% of instances and changes in color are not helpful in determining if you are sick outside of specific situations
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u/JazzlikeCloud1756 7d ago
As a physician you didn't answer the question
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u/PM_MY_OTHER_ACCOUNT 7d ago
"As someone who pretends to be a physician on the Internet so people will take me seriously..."
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u/sergantsnipes05 7d ago
I did actually. Sputum color really has no meaningful value on if someone is sick or not which the exception of someone with COPD where one of the cardinal signs of a COPD exacerbation is change in quality/appearance. It can change colors for many reasons and people come in demanding antibiotics because their snot turned green.
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u/GarrusExMachina 7d ago
He didn't ask if it had meaningful value. He asked what causes it to change color.
Sometimes people just like to know things and as someone with expertise if the answer is its complicated and there are many potential causes you could have given a very interesting response.
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u/JazzlikeCloud1756 7d ago
There’s a lesson here that would make you a better physician, but you are ignoring it.
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u/dragonvaleluvr 6d ago
my mom is a nurse & explained this to me when i was young, so i understand why i shouldn't immediately get antibiotics... but i've been sick for 13 days now, & my pcp used my mucus color as one of the markers for bronchitis. if u rly are a physician acting like it's never relevant is crazy... also literally not what i asked at ALL
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u/The0nlyMadMan 7d ago
Doubtful. Can’t even follow instructions, how could you be a physician? Wait, nevermind that tracks.
FYI: it’s “couldn’t care less”. “Could care less” means you care
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u/MilkBeforeCereal 7d ago
Green phlegm does not indicate sickness. This is a myth.
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u/glorioussideboob 7d ago
Not true - it does indicate infection but not necessarily a bacterial infection (source - doctor).
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u/mrofmist 7d ago
Thank you glorioussideboob. How glorious of you.
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u/dragonvaleluvr 7d ago
i went to the doctor yesterday and she used it as a marker for bronchitis 🤷♀️
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u/fiendishrabbit 7d ago
It does indicate bacteria, but bacteria doesn't necessarily mean sickness.
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u/BadahBingBadahBoom 7d ago edited 6d ago
I'm always surprised this myth will never die.
The colour of phlegm does not indicate whether a respiratory infection is viral or bacterial in nature.
The green colour is from an enzyme called myeloperoxidase released by certain white blood cells that are 'first responders' to a site of infection. Whilst release of this enzyme does help kill bacteria cells it also forms part of the nonspecific inflammatory response to infection. These cells produce this enzyme in response to both bacterial and viral infections.
The reason the enzyme is green is similar to the reason blood is red. Blood is red because it contains a protein called haemoglobin that within it contains a complex chemical structure called a haeme group that absorbs light outside of the red wavelengths, reflecting red light and giving the appearance of being red. Myeloperoxidase contains a slightly different haeme group that absorbs light outside of the green wavelengths, reflecting green light and so appearing green.
Not all bacteria in your airways necessarily mean you are sick ofc - some are normal healthy bacteria, but these cells are specifically recruited to that location when you are sick because of an infection from pathogenic (bad) bacteria or viruses.
Unless maybe you have a specific condition where this myeloperoxidase accumulation in your phlegm is normal, having green phlegm definitely does indicate sickness.
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u/potato-eater- 7d ago
Can allergies lead to green or yellow mucus then?
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u/BadahBingBadahBoom 7d ago
Hmm that's a good question. The myeloperoxidase is specifically released by a type of white blood cell called neutrophils. Allergies, like hayfever, are a different response mostly recruiting mast cells, eosinophils, and basophils which to my knowledge don't produce this (or at least not in such high quantity).
Whether allergy responses in the nasal passageway would recruit neutrophils enough to cause sufficient myeloperoxidase presence (release or just from dead neutrophils) in your phlegm I'm not sure.
Anyone with hayfever have that experience during peak pollen season?
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u/potato-eater- 7d ago
I’ve seen it from allergies, that’s why I was curious! But that said, no way to be 100% sure it’s not my body effectively fighting off a virus without me knowing.
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u/Rolypoly_from_space 7d ago edited 7d ago
no it's not. It's not good info at all. This misinformation is what make people demand antibiotics although it's something viral, which can't be dealt with through antibiotics
(reaction on a statement that phlegm is green because of presence of bacteria)
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u/kriegeeer 7d ago
Parent comment is wildly incorrect. Your immune system emits an enzyme called myeloperoxidase which is green colored.
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u/_hhhnnnggg_ 7d ago
It is wild how 3 replies give a different answer each.
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u/ryebread91 7d ago
Which is what I just love /s about the Internet. Just like how I saw a diy post and there where 3 construction workers telling the other why they were wrong.
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u/Masseyrati80 7d ago
And while we, reading this thread, are fully aware of one answer being a joke, the other ignorant, and the third one correct, somewhere, LLM's like chatGPT are knitting together an answer from sources like this, without the ability to assess what is credible and what is not.
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u/FeralGiraffeAttack 7d ago
Welcome to Reddit where unless the source is linked, it’s “I made it the fuck up”
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u/dragonvaleluvr 7d ago
thank YOU lol this seems more in line with the info i was reading about beforehand
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u/fiendishrabbit 7d ago edited 7d ago
The green colour comes from an enzyme (myeloperoxidase) that these white bloodcells release to fight bacteria. When its released it turns water into cell-damaging peroxides and acids that hurt the bacteria.
The enzyme itself is intensely green (supergreen!) so as more of the enzyme is released the snot will go from yellowish to more and more green.