Depends if it's an ingrown hair or a cyst.
You need to find what's causing it, in order to prevent it. Might be
hair products, or your laundry detergent or something like that.
If you're not allergic to aspirin, then do this:
Crush one uncoated aspirin tablet (such as between two spoons, or with
mortar and pestle or with a hammer, whatever), add a little water to
make a paste, and apply this concoction on the bump before bed. Wash off
in the morning.
It also helps to (orally) take some aspirin to help reduce the swelling.
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