system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is the immune system so fast to respond to allergens, but take days to fight off a legitimate infection?
gpt
Your immune system fights off most germs as quickly as it responds to allergens. 

Our bodies are invaded by germs constantly. Every breath you take. Every bite of food. Every cut in your skin brings germs into your body. Nearly all of these germs are killed within minutes or hours by immune cells that respond instantly. 

It appears to us that infections take days to fight off because we only notice the ones that get out of control, but the overwhelming majority are so quick and painless we never even know the germs were there.