How did my son become highly allergic to dogs after living with one for the first 20 months of his life??

Answer 1

Allergies don't are always appear the first time a person is exposed to the allergen.
Often, it takes several exposures until the allergy develops and becomes apparent.

"You won't have any allergy symptoms the first time you come in contact with pollens, animal dander, or other known allergens. It may take a long time to develop allergies to substances. The first time you breathe in pollen, it makes its way to your nose and sets off your immune system. Your immune system decides pollen is dangerous and makes a small amount of antibody to fight it.

But the next time you breathe it in, and every time after that, your body remembers this foreign invader and manufactures lots of antibody to fight it off. "

The more antibodies, the more the allergy "develops".

Answer 2

Sometimes allergies don't appear at the first time of exposure. The repeated exposure can bring about an allergic reaction. It's because the body is developing histamines to counter the allergen. I used to use a particular eye cream for years. They didn't change their formula but one day I noticed my eyes were itching and red. I tried everything I could think of and then finally gave up using my regular products. My eyes cleared up. I reintroduced the cream and my eyes got worse again. I developed the allergy to something in the cream over a period of time. It can and does happen.

Answer 3

Could be dandruff on the animal. Check with your vet. They have shampoos that might help