What Causes Recurring Boils With Brownish Green Discharge On Lower Stomach?

I have had reoccurring boils on my lower stomach area. They are hard knots under the skin and then pop with a brownish/green discharge. And by reoccurring, I mean about 1 a month for the 6-8 months. They pop, turn pink and the skin peels around it. Any clue why this reoccurs and what are they?