What are the common factors that trigger allergies?

Pollen dust pets. Many things in the environment can cause allergies...Pollen pets food dust bees. An allergist can be very helpful in figuring it out for you.
Genes & environment. Noses run in families. Allergy is strongly linked to inheritance. Cigarette smoking, especially during pregnancy, dramatically increases the risk of allergies in the child - even in children with no family history of allergy. Urban living. Asthma is directly correlated to living proximity to freeways and roads heavily trafficked by diesel trucks. Lack of sunshine - vitamin d deficiency are some.