Nearly anything can cause allergy problems, even heat and cold. If you have asthma, stick with your prescription meds. Asthma is a big killer in the US. People with ‘mild’ asthma die from asthma attacks too. As far as ‘natural’ remedies for allergies, outside of a placebo effect, I think one is as ineffective as the other, and you would waste a lot of money. For mild allergies, you can get a placebo effect, I know I do when I take my antihistamines. They start to ‘work as soon as I take them, before they could possibly hit my bloodstream. On the other hand, I know they are effective. Also, I would never use a ‘natural’ cure for my serious nut allergy. The micro-particles in smog are known asthma triggers, probably because of mechanical irritations, but they do not usually cause ‘allergic’ reactions. If you are exposed to several allergens at the same time, it can cause a more miserable reaction than if you are only exposed to one allergy, however, if you do not have anaphylaxis with any of them, you will not suddenly have an anaphylactic reaction just because you are exposed to several allergens at the same time, they are two different allergic pathways.