How can u develope allergies?

How can u develope allergies?
Allergies are due to the following:
You expose to a new substance or agent, scarce to your body.
It causes your body to respond next to antibodies, and to store the substance in Memory T leucocites.
Next time, the antibodies will fix to indistinguishable substance much quicker and cause a slight, moderate or severe criticism that may express itself on the skin (atopia) GI tract (intolerance to a certain food), airway (bronchi hypersensitivity), etc.
No antibodies, no allergy. Particularly you can hold an impairment to digest something (such as milk) but if it is enzymatic it is not allergy, just an impairment to digest it.
allergies recurrently develop as a result of frequent exposure.
some times your body just starts to reject it similar to when i was 12 i devolped a allergie to avacado but similar to when i was 11 i ate a avacado approaching 1 every day so i do not know but know if i put away a avacado i have to transport a epi-pen so that is how! surrounded by other words frequent exposure
yes it can be a contact problem or a genetic problem