Sty is an infection of a follicle (sac) from which an eyelash grows or of a gland in the eyelid. A sty resembles a pimple. It is usually caused by staphylococcus bacteria that enter the root of the eyelash, grow there, and form pus. Sties often occur one after another because the germs spread from one hair follicle to another. Rubbing the eye may spread the bacteria more quickly.
White blood cells in the body usually kill the germs that cause a sty. Then the sty softens, breaks, lets out the pus, and heals. In some cases, the pus may have to be drained by minor surgery. When sties continue for a long time, doctors may treat them with antibiotics. Doctors can prevent sties from occurring with a vaccine made from staphylococcus bacteria.
