Well, if I could answer that, I could be a billionaire!
Keep in mind that each of us is different, but here is my short story.
My diagnosis is asthma, bronchiectasis and hyper reactive airways, and here's what causes exacerbations for me - stopping airway clearance, viral respiratory infections like a cold, getting extremely stressed and overtired, not managing my asthma & allergies, being exposed to smoke (like this summer's fires) and some chemicals. I will get inflamed airways, bronchitis, pneumonia or even pseudomonas (I think that is always lurking in my lungs, along with MAC, but grows much faster.)
If I catch it immediately & treat with extra levalbuterol & saline nebs, extra rest and lots of good fresh fruit & vegetables, I can sometimes recover spontaneously. If not, it is on to steroids and antibiotics.

Can you figure out your triggers based on your most recent exacerbation?
Sue

my exacerbation this week was caused by a “cold” not covid. I waited a week, it then felt like fatigue and a low grade fever would keep me from my normal routine for another week or ???? I had a script for 7 days of doxycycline for an “exacerbation “ if it happened on a trip. I started it yesterday and am starting to feel better already. Has anyone else used this? I also turned in a sputum culture before I started antibiotics so I could review with my doctor later.