What is causing white powder on walls and walls near air purifier's and humidifier and is it a health issue?

The white powder on walls near air purifiers and humidifiers is often caused by mineral deposits from hard water vapor, which can settle as the moisture evaporates. These deposits are typically made up of calcium and magnesium, and while they may be unsightly, they are not generally considered a health issue. However, if mold or mildew is present due to excess moisture, that could pose a health risk. Regular cleaning and maintenance of appliances can help minimize these deposits and reduce potential issues.