Non-blister sore on the labia majora that is recurring…?

My friend is experiencing a recurring “sore” on the labia majora. Symptoms include pain when touched, and a lump beneath the skin. There is no pain when urinating and she says it definitely not a blister, nor does it scab over when it starts to disappear. (I asked her these questions thinking it may be a Herpes outbreak.) She says, too, that there is no abnormal discharge or scents when this occurs. She says she has been tested for STD’s including Herpes and Genital Warts – all returning a negative result. She stated that the sore seems to always appear in the same spot. The times that it does appear seems to be sporadic: sometimes during her menstrual cycle, other times just “out of nowhere”. It’s not a monthly occurance…sometimes she goes a couple of months without any signs.

If anyone has experienced this or knows of someone who has, I would appreciate any input you have to offer.

She has a sebacous cyst. It’s not infectious nor a STD. She can leave it alone or go to the Doctor next time it occurs and see what her options are. Surgery, might not be required. The doctor might put her on hormonal therapy

Genital Herpes Pictures