I get sebaceous cysts in my crotch area, but I've not previously ever gotten one anywhere else. How does one know when a lump is just a sebaceous cyst and when it's something to worry about?

I have no idea if anyone else in my family gets them. I've never thought to ask. Well, I know my step-father has a huge cyst on one of his arms, but that's not pertinent to my inheritance of the tendency.