What causes ovarian dermoid cysts?

Not known!: Hello, we don't know why ovaries make their cysts. Seems that they are a very active organ, what with making eggs and hormones, and sometimes the egg-making cells just overgrow and become a dermoid cyst, complete with hair, skin, and other cells that the 'germ cell' (egg producing cell) has in it's potential. Wierd, huh! they are benign, but don't go away without surgery, and can be recurrent.