The American Dental Association recommends getting a new toothbrush (or brush head, if you use an electric toothbrush) about every three months–more because of the wear on the bristles than germs.
With bristle wear being one of the main reasons for replacing your brush, they also harbor bacteria. If not cleaned effectively, microscopic bacteria can reside on your toothbrush. After time and several uses, toothbrushes will lose their effectiveness. Once the bristles begin to wear down, they are not as efficient at cleaning plaque and removing food and other debris from your teeth. It is also suggested that you change your toothbrush after any type of illness, such as a cold, the flu or any type of mouth sores.
You should always rinse your toothbrush after use and let it air dry in an upright position. If you are really worried about germs and bacteria, you can soak your toothbrush in alcohol, or mouthwash as it is also an antiseptic. Another option would be to dip your toothbrush in boiling water for 5 to 10 seconds. Never put your toothbrush in the microwave or the dishwasher, as both these methods will damage your brush. Children’s toothbrushes may have to be replaced more frequently, as children tend to be heavy handed when it comes to brushing and the bristles on their brushes wear out sooner.