The optimum level of humidity in a home is 45 to 65 percent.
Dry air in the winter is one the main causes of sinus infections and sore throats. You can use a mechanical humidifier to add moisture to the air, but you can also invest in indoor plants.
To add humidity to a room you can place a few areca palms inside. These palms release copious amounts of water into the air, and remove chemical toxins too. They are consistently rated among the best houseplants for removing all indoor toxins tested.
According to B. C. Wolverton, author of How To Grow Fresh Air, a six foot (1.8 m) areca palm transpires approximately 1 quart (1 litre) of water every 24 hours. So if you put three in your bedroom, the palms will be release three quarts of water per day — not bad!