Question: how is some people allergic to things others aren't allergic to

Christie Waddington answered on 17 Jun 2016:

Mostly because of your genes. There are some people who are more likely to develop allergies because they have certain mutations. This is called “atopy”. But this isn’t the whole story!

If you lived in a very clean house when you were a baby (before you were 2 years old) then you are more likely to have allergies because your body didn’t develop the immune cells early on. How old you are where you are exposed to things e.g. cats and dogs is also very important.