Are humidifiers very helpful for asthma?

For some: Especially if there is a major allergic component, humidifiers can help. More likely to help in dry areas of the southwest.

Probably not: Humidifiers and vaporizers add moisture to the air but this added moisture has little effect beyond the nasal passages. Adding moisture to the bedroom environment encourages growth of houses dust mites and molds not usually considered beneficial for persons with asthmatics. I generally discourage the use of humidifiers & recommend dehumidifiers.