What causes allergies and how does the immune system react?

Allergies happen when your immune system gets confused and overreacts to something harmless, like pollen or chocolate.

Imagine you're playing in a sandbox, and suddenly a big pile of sand falls on you, that's surprising, but not dangerous. Your immune system is like a guard dog who usually stays calm unless there's a real threat. But sometimes, the guard dog sees a little bit of sand and thinks it’s a monster! It barks loudly and runs to attack, making you sneeze, cough, or feel itchy.

Now imagine that allergen, the thing causing the allergy, is like that pile of sand. When you touch it or eat it, your immune system thinks it's a danger and sends out tiny helpers called white blood cells to fight it off. This causes the symptoms we know as allergies: runny nose, watery eyes, or even hives.

Sometimes, the immune system gets so excited that it makes too many helpers at once, like if all your friends showed up to help you dig through the sandbox and made a big mess! That's why some people get really bad reactions from something small, like eating a peanut.