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How large was the bump before it expelled its contents. The closest possibility which matches your description is a sebaceous cyst
. Sebaceous cyst is a cyst arising from swollen hair follicle. It contents cheesy like material. Though a non concerning problem, it has high rates of recurrences. Chances of recurrence are high when there is incomplete evacuation of its contents - like what happened in your case.
Besides this, a secondary infection may occur resulting in worsening of the condition.
So I am concerned with it and I advise you to see your doctor at the earliest. Your doctor may plan a safe removal to prevent recurrence.
Hope this answers your query.