What can you tell me about allergies?
Allergies are usually caused by a hypersensitivity of your immune system to your surrounding environment, so it could be caused by many things.
Have humans always had them?
It seems like it is possible, especially having symptoms like red eyes, a runny nose, and sneezing! Luckily there are products to help ease those symptoms.
What percent of the population deals with it?
I am not sure the exact numbers, but I know the numbers seem to be rising for kids with asthma and food allergies. 
How is it treated?
Some people go through allergen immunotherapy where you are actually exposed large amounts of the allergen to change your body's response.
That's interesting. Do people ever die from allergies?
Perhaps if people go through the allergen immunotherapy the benefits could last for years after treatment, which would help future generations.