There is a pustule on the front of one side of the external genitalia, and it's a bit hard. What could be the reason?

Patient's question:

Currently, in general: No fever, no other discomforts
History of previous diagnosis and treatment, as well as effectiveness: Not treated

Doctor's answer:

Considering the possibility of vulvitis, it is recommended to go to the hospital for comprehensive examinations to further diagnose the cause and cooperate with treatment. In daily life, maintain cleanliness and dryness of the vulva. Avoid scratching, hot water washing, and using soap. When infected, use potassium permanganate solution for Sitz baths. Underwear should be breathable and loose. Avoid alcohol and spicy or allergenic foods.