Styes are minor, short-term bacterial infections affecting the edge of the eyelid or eye. A stye is also called a hordeolum.
Glands around the edge of the eyelid get clogged and swell until a sore like a small pimple or boil appears. It may also be due to a blockage in a follicle of an eyelash. The sore causes eye pain and becomes temporarily filled with pus. A second, more serious type of stye can develop deeper inside the eyelid and swell until it needs the attention of a doctor.
Styes are the most common type of eyelid infection. The average person has a good chance of having one or two styes in their lifetime, though some people develop them repeatedly. They can be annoying and painful but are usually not serious.