I had allergy/chemical sensitivity problems in 1986 when we moved into a new house with new blue carpet. I was thinking it was the carpet dye (I thought maybe the blue dye was somewhat unusual). About 5-10 years later, it was discovered that the glues used in carpets (even the ones not glued to the floor) caused major problems in some people.
Then in 1990, I developed asthma when the office building I was in was rehabbed while it was occupied. The problem was most likely dust and mold being thrown around the air. I could no longer stand to be anywhere near anyone smoking, or wearing most fragrances (floral perfumes, right guard deodorant, and more recently Axe spray are particularly bad). Gasoline fumes can cause an asthmatic reaction. The asthma medications don't help much. I've always been allergic to Dial soap and Tide detergent, all detergents with fabric softener included, and the fabric softening dryer sheets; the reaction is itching all over. At times I've been in rooms with particleboard furniture, and it's awful. Even our newer office with supposedly low emission particleboard and carpet was particularly bad for the first few months.
So, you learn the things that set off your allergies or asthma, and avoid them as best you can. I have to avoid anything that says "New Improved Fresh Scent." or anything like that.