system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do new allergies develop?

How do people start developing allergic reactions to things they weren't previously allergic to?
gpt
I was taught to think of the immune response like a police traffic stop.

An unknown protein is driving along, and gets pulled over by a police officer because it "doesn't quite look right". Everything is fine and the protein is allowed to continue. The officer files a report that they did the stop and this is put on the police computer.

That protein is seen again and when a police officer sees it, it sets off an alert because it had been stopped before. The police officer tries to stop it to see what is going on. The protein is allowed on its way, and another report is filed.

Later on, the protein is seen again. A police officer sees it, and sees that there have been several stops made, so he gets quite twitchy and stops it with even more force. It is allowed on its way as it is doing nothing wrong, and another report is filed.

The protein is seen again, there are huge red flags because of the amount of times it has been stopped and the level of force used when it has been stopped. an armed response unit is sent to stop it. Nothing amiss happened, so it is allowed on its way.

The next time it is seen, an armed response team is deployed again based on past stops, it is surrounded and forceful entry is effected damaging nearby structures as the police raid where the protein is to see what is going on and why it has so many markers against it.

&#x200B;

The protein itself is doing no damage, but the immune response is having the negative effect on the body systems. The immune response increases with each exposure, leading to more damage on the systems.