My sister is 15. she got a sudden red bump on heresy nipple and it doesn't hurt. what could it be? it looks infected in the center of the bump.

Moist heat, review: Superficial infections of the areola complex are frequent. Sebaceous oil glands are present in the skin. The skin is quite thick and durable, thus leading to the problem of local infection of these small glands. Local moist heat with a wash cloth with hot water 3-4 times per day along with witch hazel as a skin lubrication may help. Surgeon review with lance, drainage, antibiotics maybe needed.