<s>[INST] I sometimes get these lumps in my armpits that feel like a little ball under my skin and have a black head on the surface. I squeezed one out and this White substance came out behind the blackhead? What are they, why am I getting them and is there anything I can do to prevent / treat it? Thankyou for your help. [/INST] Hi,From history it seems that you might be having infected sebaceous cyst giving this problem.consult surgeon and get examined.If cyst is there it requires excision the cyst with sac to get complete cure.Ok and take care. </s>