A stye - or sty - is a common bacterial infection that produces a pimple-like boil on the eyelid or near the edge of the eye. A stye is caused by the staphylococcus bacteria, which infects the oil-producing glands in the eyelid that lubricate the eye.

Common symptoms of a stye include:

• A red, painful bump on the eyelid that looks like a pimple or boil
• Tenderness of the whole eye area
• Swelling of the eyelid
• Crusting near the eyelashes
• Light sensitivity
• Tearing

A chalazion - clogged pores in the eyelid - may cause similar swelling, but rarely produces the coloration and pain that a stye does. A chalazion commonly occurs on the inside of the eyelid, where styes usually appear on the outer skin of the eyelid.

Styes can be prevented with good hygiene and self-care methods such as:

• Wash your hands, especially before touching your eyes
• Wash your face before bed
• Wash off eye makeup before bed
• Wash your hands before and after removing contact lenses. Disinfect multi-use contact lenses before wearing them again, and discard limited use contact lenses after taking them out.
• Throw away old or expired eye makeup
• Do not share eye makeup

Styes are very common and usually go away within a few days. The infection rarely causes any serious medical condition aside from swelling and pain in the affected eye. However, if redness and swelling begin to spread to the rest of your face, talk to a health care provider right away.