Have you ever been outside playing and suddenly started sneezing a lot or your nose starts running? That's called "allergies" and it happens because your body is hypersensitive.
You see, your body has a special system to protect you from bad things like germs and viruses. It's called your immune system. It works by detecting when there are bad things in your body and trying to get rid of them.
Sometimes, though, your immune system gets a little too excited and starts reacting to things that are not really bad for you. These things are called "allergens," and they can be things like pollen, dust, or even certain foods.
When your immune system reacts to these allergens, it can cause lots of uncomfortable things like sneezing, itching, rashes, and even trouble breathing. This is called "hypersensitivity" because your body is being too sensitive to things that aren't actually bad.
If you have allergies, don't worry! There are lots of things you can do to feel better, like taking medicine, avoiding things that make you feel bad, and even getting allergy shots to help your immune system calm down.