A nebulizer is a device used to deliver liquid medicine in the form of a fine mist (aerosol) or powder. Medicine may be given through a nebulizer to treat respiratory problems, such as asthma, chronic obstructive pulmonary disease (COPD), or pneumonia.

The nebulizer allows the medicine to go directly to a person's airways and lungs, and the medicine can be given over a long period of time. The person inhales the medicine while breathing normally through a mouthpiece or face mask. A nebulizer makes inhaling medicine easier for people who are having serious difficulty breathing or who have trouble using an inhaler, which requires careful timing and control of one's breathing.