Hi - We've lived in our house for the past 4.5 years, & have never had this problem in the past. Our house was built in 1951 & has plaster walls. We have a small bathroom, which has never had a fan installed. For some reason, small bubbles (ranging in size from 1/2 inch to 2 inches in size) have formed all over the bathroom walls & ceiling. Now, there are some in the hallway where the wall & ceiling meet as well. We do have a/c ducts running through the house. When we pick the bubbles, there is a little moisture underneath, but the plaster seems to be dry. Any ideas as to what it could be? My husband does take really hot showers, but that's nothing new & we haven't changed anything in the bathroom in the past 4 years (we just open the window).