A pustule is a small, pus-filled pimple. Pustules usually appear as pale or red lumps with a white center. The skin around them may be inflamed and sometimes itchy or painful.
Pustules are a feature of a large number of conditions, probably the most common of which is acne vulgaris, although sometimes an isolated pustule appears without any apparent cause and then disappears spontaneously.
A sudden outbreak of a large number of pustules may indicate an underlying disorder and should be seen by a doctor.