How can humidity affect asthma? two times my bf came out of a hot shower, having trouble breathing but became fine as soon as he left the bathroom.

Depends: I have had many patients state that their asthma worsens when outside in hot and humid weather, especially when exercising. Cool dry air is a more typical asthma trigger. If this is happening to him i wonder whether his asthma is giving him trouble in other ways as well? Perhaps he should try shorter and/or cooler showers.

Asthma: I agree with dr. Glauber, but you also need to know that asthma is a very serious condition...If he has a real diagnosis of asthma. If he does, and he is still having symptoms, he needs to see an asthma specialist to get his breathing under control. If he is already on medication, then his meds need review and he might need better or stronger therapy.