In medicine, a cotton swab is a small piece of material, such as gauze or cotton, which is used to clean wounds, apply medications, or retrieve samples of body fluids such as blood or mucus. Swabs may be attached to stiff wires or sticks to aid access. Swabbing is useful as a noninvasive technique which is easily mastered. It's also used when dealing with bacteria.
Swabs are also used for cleaning and/or testing in other fields, such as the dyne test of the surface energy of plastics. It has been found that swabs made by different manufacturers can give different results, because different substances are used to bind the material to the stick