Inhaling steam when you have asthma can help with the asthma symptoms.
However breathing in steam is not a cure for asthma so if you're having an asthma attack you need to get medical attention and use your inhaler when you need it to prevent the asthma attacks from happening.
Although steam does help some peoples asthma there has never been a study to prove through science or medically that steam helps with asthma.
However my friend has asthma and she uses steam to help with the asthma and it does help but the steam is not a cure for the asthma.
So you need to use your inhaler prescribed from the doctor for asthma to help prevent an asthma attack or when you feel an asthma attack coming on you need to use your inhaler.