eli5: what happens on a cellular level when someone has an allergic reaction?
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Usually, your immune system thinks the allergen is the deadliest murder-germ ever and goes into maximum overdrive trying to fight it, causing collateral damage all over.
This, the collateral damage as well as your body going into overdrive, is what manifests as the allergic reaction.
An allergic reaction is your immune system reacting to something that is otherwise not dangerous.
Pollen or pet dander getting in your nose or eyes? Better crank up mucus and tears to collect all of that foreign material to get rid of it.
Nickel on your skin? Better make a rash so my body gets away from it.
Penicillin in my body? Better get all the troops out to fight it off (anaphylaxis).
Antihistamines are usually used to treat mild allergies because histamines are the part of your immune system that responds to it. As for anaphylaxis, I’m not really sure what’s going on other than a lot of swelling.
Other responses have answered the question better than I could but I want to add a pedantic point that allergies don’t really happen at the cellular level. An individual cell can’t be allergic but a bunch of cells together signaling and mounting an immune response create an emergent phenomenon
Most of symptoms that you experience during an illness is produced by your own immune system to fight an infection.
Fever, runny nose, coughing are your body trying to get rid of the pathogen.
Also your immune system has some pretty nasty trained killers, that are very good at their job, that is killing cells. Unfortunately you are made of cells and sometimes the killer cells do collatheral damage killing healthy cells.
Even your immune system can go so overboard, that it kills you, Like Auto-immune diseases.
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As for allergens, your body misidentifies allergens as pathogens and it starts to attack it, more and more drastically. The problem is that it doesn’t really work, since they are not bacteria or viruses. When reaches the carpet bombing state with inflamation and hystamine release, it starts to get really dangerous, your immune system is raging killing anything and everything around the allergen.
Anaphylaxis is when your life is in danger, your heart is in overdrive, you are inflamed allover, breathing starts to get hard even impossible. There is a hight chance that you die.
Your immune system’s job is not to keep you alive, it’s job to kill foreign invaders.
You need high dose adrenaline, which opens up your airways and increases your blood pressure.
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I would suggest watching “Cells at Work”, it is a little oversimplified but does a decent job to show the basics of the immune system
It has a dedicated episode about allergies
This one is for anaphylaxis
Your immune system has made antibodies against something that wouldn’t cause infection. These antibodies (IgE) are attached to mast cells (a type of immune cell) and some other immune cells, but mast cells are the main one. When you are next exposed to the allergen, the antigen (the part of the thing you’re allergic to such as a protein) attaches to these antibodies. That then triggers the mast cells to release lots granules stores within them. These granules contain things like histamine, nitric oxide and other substances that are what cause the symptoms of anaphylaxis. Because there are such massive amounts of these substances and that they are in the blood so they get transported all round the body quickly you get a sudden and widespread effect.
These effects include causing airways to constrict. Blood vessels dilate (widen) and your blood pressure drops because it’s like trying to fill a much larger area with the same amount of fluid. You also get swelling of tissues (another reason bp drops as fluid moves out of the blood into the area of swelling).
It’s the immune system going into over drive
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