Can an allergy disappear and come back?

[Allboxedin]

Morning!
DD had a milk allergy up until about 12 months amonst other things (egg,wheat,fish,nuts etc) and was put on a prescription milk (Nutramigen)
She seemed to grow out of it by about 12 months and has been fine with cows milk since.

Now she is 2 next month and she keeps coughing after what we think is milk, (although we are unsure if it's the milk) there are no other signs like she had before like being sick,hives etc,it's just this bout of coughing she has after drinking.
She has an appointment with the paediatrician coming up in October as she has been having problems with viral induced asthma but I wondered if anyone had experienced an allergy returning after having disappeared?

It's not the same but I have a allergy to conifer trees that comes and goes. We had lots in out garden and sometimes I'd play in and round them and would get nothing, other times I'd brush gently on one and come up in hives all over where I'd touched and beyond. Still like that now.

I find allergies so complex and unpredictable :(