Humidifier is a necessity of winter in Japan. In winter in Japan, the air is dry. And when you using heating, the humidity further decreases.
Drying may cause skin roughness or skin cracks. Also, when temperature and humidity are low, you will catch a cold easily.
If you are using a stove, please put the kettle with water on the stove. It will be a substitute for a humidifier, as hot water evaporates.