One of the easiest ways to get rid of humidity in your closet is to add a small dehumidifier. A dehumidifier removes moisture from the air to create a drier environment. The most typical model uses a refrigeration unit that contains an exposed cold coil. A fan draws moist air over the coil so it can be condensed and the condensed moisture is released through a drain or collected in a container that can be emptied. For a closet, choose a smaller model so you can still access your clothing, shoes and accessories while it is in operation.
Another way to reduce the humidity in your closet is to install an exhaust fan in the ceiling. A small bathroom-sized model is usually adequate for an average-sized closet. Purchase a fan that can be programmed to turn on and off throughout the day so the air circulates even when the door is shut. The moisture-laden air will be forced out around the door so the closet loses some of its humidity.
In a small closet, a strong light may be sufficient to dry out humid air. A ceiling mounted fixture that can house a 60- to 100-watt bulb can help heat the air in a smaller space and remove moisture. The drawback to this method is that the light must be run continuously to effectively dry the closet so it is not an energy efficient practice.
A box of ordinary baking soda is a simple, inexpensive solution to your closet's humidity problem. Place an opened box on a shelf or the floor of the closet. Just as it absorbs odors in your refrigerator, the baking soda absorbs moisture from the air and helps create a drier environment for your closet. It will also remove any musty odors that plague the space.
If you grill in the summer and a have a leftover bag of charcoal, it can help with a humid closet as well. Like baking soda, charcoal is a highly absorbent material, so it can help remove moisture from the air. Add several briquettes to a piece of cheesecloth or small mesh bag and place it on your closet shelf. You may also hang the charcoal from a hanger or hook if it is more convenient.