I developed allergies and asthma seemingly out of the blue at around 8 years old, and my allergies grew in scope over time. At first I was just allergic to cats, but eventually that became all animals with fur or feathers, tree pollen and dairy.

It's just speculation but in my case I think the factors at play were: Genetics - nobody in my family has allergies but eczema and psoriasis are in the family and that can lead to higher chances of developing allergies Smoking - my mother smoked while pregnant and for years after I was born. Grandparents were chain smokers too so I was exposed to tons of second hand smoke Antibiotics - I don't know why or exactly at what age but there was a time when I was constantly getting ear infections (doctors often remark on the scars when they look in my ears), so I was on antibiotics all the time. If there is a natural balance of fungi and bacteria in our bodies, that was surely thrown off.

Today my asthma is mostly cured, I keep an inhaler just in case but use it less than once a year, but my allergies haven't improved at all.