A stye is medically defined as a painful, red lump, looking similar to a pimple formed close to the edge of the eyelid, on the outer part of the eyelash line. They can sometimes appear on the inner part of the eyelid; in which case they will be further from the eyelashes base. Most individuals experience them one at a time, but you can sometimes develop styes in both eyelids at the same time. Generally, they disappear on their own within days, but there are several actions individuals can undertake to ease the discomfort and diminish associated pain.
Internal vs external styes
There are two types of styes, differentiated based on the location they form in.
External styes are the most common and they begin in the follicles of eyelashes, or, occasionally in the sebaceous gland, also known as the oil gland. External styes are associated with the Zeis or Moll gland. The Zeis gland has a key role in preventing the hair follicles of they eyelashes from drying out, by secreting oil. The main cause of external styes is the bacterial infection caused by Staphylococcus.