Why do people get allergies they didn’t have previously? How do you become allergic to something that was perfectly fine before?
In: Biology
Our current understanding of allergies is that they are a defect in a person’s immune system. The body decides the trigger (an “allergen”) is some form of infection so it starts sending the immune system after that. In really bad cases it thinks the infection is so powerful it ramps up the immune system so much the side effects are fatal. Evolution is not very smart, it just gets to roll the dice a lot.
The immune system “learns” and changes over time. Also, as we age, our body’s cells can accumulate damage and defects in their copies of our DNA.
So sometimes when we encounter an allergen, the body gets mad, sends the immune system, and for whatever reason that one thing makes the body say, “Wow, that was bad, next time I see that I need to fight harder.” That means each time the person gets exposed, they’ll be a little more sensitive. From what I understand the oil in poison ivy works this way: repeated contact tends to eventually start resulting in reactions.
Other times the DNA changes/damage over time makes the immune system behave stupidly when it sees something it used to see as benign. This is kind of like how cancer forms, it’s unpredictable and we can’t really detect or stop it.
Other times, a virus/infection like COVID-19 does damage that changes the immune system. One of the ways people die from COVID is sort of like your immune system deciding your *organs* are an infection that must be destroyed. COVID does this damage to help protect itself from the immune system. Sometimes it overdoes it and the host dies, taking that strain of COVID down with it. Like I said, evolution’s not very smart. (We’re also learning some viruses can cause “immunity erasure”, making your immune system literally forget how to fight other viruses. Measles can do this, and we didn’t really know until recently. We’re sort of curious if we can hack this process to “fix” damage like this but it’s kind of a new thing, the COVID research is some of the first practical work that uses the ideas.)
So it’s a side effect of three things:
1. Our bodies aren’t perfect, and over time our DNA “blueprints” get more and more corrupted, which creates unpredictable problems.
2. The immune system is supposed to be flexible and “learn”, but just like a kid watching the wrong Youtube videos it can get the wrong idea and cause problems.
3. Some people are born with immune systems that have bad ideas that only get worse over time.
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