The main differences between the humidifiers and dehumidifiers are:

Purpose:

• The purpose of a humidifier is to increase the moisture in the air.  
• Dehumidifier purpose is opposite to humidifier as it decreases the humidity in the surrounding areas.

Humidity level:

• A humidifier is used where humidity is less than 35%.
• A dehumidifier removes moisture from the air when it is too humid or above 50%.

Usage:

• A humidifier is mostly used in cold weather (especially during the winter season) because the air is too dry or cold. Thus, having the moisture in the air makes the skin moisturized through the winter season.
• Dehumidifiers are mostly used in the warm or summer season because the air is hot and have a high level of humidity. The humid air level can cause moulds and mildew, and the bacteria from these can cause headache and flu. Therefore, the decreasing humidity would also reduce the build-up of such toxins.

Types:

• There are two major types of humidifiers: warm and cool mist that works very differently from each other.
• Electronic, refrigerative (also called mechanical), desiccant and ionic are the types of dehumidifiers.