Excessively low humidity may occur in hot, dry desert climates, or indoors in artificially heated spaces. In winter, when cold outside air is heated indoors, the humidity may drop as low as 10-20%.
This low humidity can cause adverse health effects, by drying out mucous membranes such as the lining of the nose and throat, and can cause respiratory distress. The low humidity also can affect wooden furniture, causing shrinkage and loose joints or cracking of pieces.
Many homes can become low in air moisture, especially during the winter months. In fact, furnaces and other heat can add to the dry air.

A humidifier is a household appliance that increases humidity (moisture) in a single room or in the entire house. There are point-of-use humidifiers, which are commonly used to humidify a single room, and whole-house or furnace humidifiers,  furnace humidifiers which connect to a home's HVAC system to provide humidity to the entire house.
There are portable humidifiers that can be used to control moisture in a room, but there are also full house humidifiers that can be added to your HVAC system.
Humidifiers and electronic air cleaners are two HVAC accessories that can easily be retrofitted to almost any existing HVAC system.
Both are economical and will vastly improve the comfort of the occupants, as well as the indoor air quality of the home, which impacts the health of the occupants, especially those with allergies, asthma and other respiratory health issues.  -  See more at:humidifiers

Therefore, to making the air in your home easier to breathe, a humidifier can put an end to dry winter skin and hair.

In addition, because heating dry air is less efficient, the installation of a humidifier can also make a noticeable difference in your winter energy bills