If your furnace doesn't have a built-in humidifier, you may rely on a portable room humidifier to restore moisture to the dry air in your home. While very low room humidity can lead to increased static electricity and itchy skin, it is better than using a less-than-clean humidifier, which can lead to illness.
Mold and bacteria can breed in room humidifiers, according to Mayo Clinic, and it can get into the air through the mist when the unit is turned on. When contaminated mist is inhaled, it can cause breathing problems, asthma or allergy attacks, and infections.
This is especially dangerous for the very young, elderly people or those with compromised immune systems. If you notice scum or film that floats on the surface of the water in the tank or if it is evident on the bottom or sides of the tank, it may be contaminated with fungi or bacteria.
If your humidifier has developed crusty or scaly material inside the tank it may mean that microorganisms are also growing. Scale and other deposits are mainly comprised of minerals, which create a hospitable environment for mold and bacterial growth. These minerals can also become attached to the mist, and when the humidifier is turned on, the mist, along with the mineral deposits can be expelled into the air, and into your lungs.
You can also develop skin irritation and rashes from being exposed to a dirty humidifier. This can happen when the airborne mist comes into contact with your skin or when you touch the apparatus to add more water to the tank.
If your skin becomes red, inflamed, irritated or itchy, or if you notice welts, blisters or peeling, see your doctor. In rare cases, dermal symptoms such as hives can be early signs of a life-threatening condition known as anaphylaxis, which can also cause swelling of the lips, mouth, throat and tongue. This dangerous condition occurs when susceptible people are exposed to certain allergens.
To reduce your risk for illness, change the water every day so that scale or film doesn't have a chance to develop. Do not add fresh water until you have removed the tank and cleaned it with hot, soapy water. If the manufacturer's instructions recommend that you use household bleach to clean your humidifier, make sure you rinse it thoroughly to avoid inhaling chlorine fumes from the mist.
To reduce the risk of mineral deposits and scaling, do not use tap water to fill the tank, but instead, use demineralized water. If your humidifier comes with filters you can use tap water because the minerals will get trapped inside and won't get deposited into the water. Also, when storing your humidifier for the summer months, make sure it is cleaned thoroughly so that mold doesn't grow inside the filters and motor.
If your humidifier's motor appears dirty, scaly or calcified despite your best efforts at cleaning, it may need to be replaced. If your finances allow, consider a built-in humidification unit that becomes part of your heating and cooling system.
Call a furnace contractor to discuss your options. If you already have a humidifier built into your furnace system, schedule periodic maintenance appointments to make sure that your unit is in good working condition and that it is clean.
A faulty humidification system can also cause mold growth to develop in your duct work, which is especially dangerous because you are unable to see it. If you are worried about this, a heating and cooling professional can investigate further to determine if your home's environment is in danger of mold spore infestation.