What causes your body to suddenly develop an allergic reaction to something later on in life that you weren’t allergic to before?

Question

i.e. how does ur body suddenly decide something is dangerous enough to warrant a reaction even tho it didnt cause it before

i might be using these tags wrong yeesh

In: 42

Answer 1

I am not a doctor but have a hypothesis. For reference no one really knows.

So there is a process called molecular mimicry where your body can recognize two similarly shaped molecules as being the same molecule. One example is oral allergy syndrome (I have it) where your body responds to a protein in plant pollens you’re allergic to like birch pollen; then finds similar proteins in certain families of fruits or vegetables and gives you a mild food allergy. Birch pollen is associated with apples, peaches, cherries.

Another example was when a bunch of people got narcolepsy from a flu shot it the early 2010s. It only happened to like 200 people out of 2 million doses, very weird. Their body picked a specific protein in the flu virus to attack and neutralize it, that protein was very similar to one that regulates sleep in humans. Just like that their immune system learned to attack a the protein that keeps them awake at normal times.

So my thinking is that many allergies probably come from our immune system learning m a way to destroy a pathogen, but the proteins it chooses to attack in the pathogen share a similar shape to a protein in something we eat, which after that infection may become an allergy. Why doesn’t everyone who gets cold X become allergic to ragweed? Because there are hundreds of proteins in any given pathogen which your immune system can choose to attack in order to disable it, and not all are similar to things we eat or breathe in.

Again I’m not a doctor or a scientist, just a guy who enjoys a puzzle.