Whole house humidifiers and portable room units can be a good way to add back the necessary moisture to the air in your home, preventing allergy & asthma attacks, and other respiratory problems. There is something to be careful of, however: since a whole house humidifier is adding moisture to the air going through the duct work (where mold & bacteria often live), if you don't have a UV light system that's killing those mold spores and bacteria, you're feeding them the moisture they need to multiply and grow, which can flood your house with ten times the airborne mold and bacteria that you had before the humidifier was added.
A lot of home owners don't realize it, but the ducts in our homes, unless brand new or recently cleaned (within 2 months) is usually loaded with dust mites, viruses, pet dander, and other pollutants, as well as live mold spores and bacteria. Those live mold spores and bacteria tend to live pretty well there because there's lots of organic material to feed on, as well as moisture from the cooling coil. And we're talking about the duct work after the filter-between the unit and your floor vents, so no, the A / C filters can't remove anything from this area. And adding more moisture to the ducts feeds these mold spores and bacteria even more, which can cause them to multiply quickly and create some real health hazards in your home.
You can, however, use a whole house humidifier, if you have a UV light air cleaner installed in the duct. Top-rated UV or ultraviolet light air purification systems use laboratory grade 36 watt bulbs that deliver enough light units to destroy over 95% of virtually all strains of bacteria and mold, even algae. So, if you have one of these UV systems installed in your HVAC or central air conditioner system duct, that is going to kill any mold spores and bacteria that float by, and add OH- ions to the air, which also kill any mold and bacteria wherever they are in the duct work, stuck to the inside walls, etc. This way, you can enjoy that added soothing humidity you need, without creating a health hazard for you and your family.
UV light air cleaners are very effective for reducing sinus and respiratory problems, in general, so if you have any conditions like this, you might find some added relief from having both the necessary moisture and NOT having any more mold spores or bacteria floating around to continuously re-infecting you. Duct mounted UV air purifiers are also good for reducing odors, since the OH- ions tend to neutralize those, as well.
So, especially if you're thinking about buying a whole house humidifier or you're using a portable room humidifier now, consider adding a UV light system to your central air conditioner, to make sure you're getting the best allergy or respiratory relief You can get-without feeding bacteria and mold spores (and viruses) that are usually the problem.