The exact causes of allergies and asthma are unknown, but yes, experts do believe that many aspects of modern living are a factor, as is climate change.   Things that trigger (not cause) asthma in already sensitive people can include: --dust --pollen --animal dander, saliva and urine --molds --insect droppings   Many people are not allergic to those things, but for unknown reasons, some people are. Their bodies go a little haywire interpreting normally harmless substances as harmful. We know what happens in the body as a result and we know who is most at risk for allergic disease, but we still don't know why some people become allergic, while others with the same risk factors and exposure do not. It's still a bit of a medical mystery.   Risk factors can include: -- environment -- family history of allergic disease -- exposure to secondhand smoke -- certain prenatal factors   But those are only risk factors, not a guarantee.   Does that clarify?   Best, Kathi