NinjaNeer answered Tuesday July 6 2010, 8:31 am: I have these, and so does my mom. It might be a sebaceous cyst.
Your mom's right - it does look like a pimple, because that's basically what it is. The difference is that the material inside is sebum, which is an oil produced by your skin, and it's located further down in your skin layers.
Fortunately, it doesn't usually cause problems. Sometimes they can grow too much and rupture, or they can get infected. You can get rid of them with surgery, or you can also try applying a heating pad several times a day.
I checked out the Wikipedia entry to make sure it didn't have any really gross pictures:
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