A stye is a small, painful, red bump on the edge of the eyelid that is similar to a boil or a pimple. It is caused by a bacterial infection in one of the small glands near the base of the eyelashes. The bacterium staphylococcus is commonly responsible for most of these infections. A stye usually forms when a tiny oil-producing gland in your eyelash follicle or eyelid skin becomes blocked and gets infected. Styes are often filled with pus and can be on the outside or inside of the eyelid.

Some factors that can increase the risk of developing a stye include long-term blepharitis (inflammation of the eyelids), poor eyelid hygiene, and using old or expired cosmetics. To reduce swelling and help the stye heal, a clean flannel soaked in warm water can be held against the eye for 5 to 10 minutes, repeated 3 or 4 times a day. Painkillers such as paracetamol or ibuprofen can be taken to relieve pain. It is important not to burst a stye or remove an eyelash as this can spread the infection. If a stye is very painful or swollen, does not get better within a few weeks, or affects vision, it is recommended to see a GP.