Both of my young daughters have dermoid cysts on their ovaries that require surgery. what advice could i offer them to avoid this in the future?

Ovarian Cyst: Dermoid cyst cannot be prevented. I would recommend consulting a good Gynecologist and deciding what is the best course of action.

Dermoid Cysts: Dermoid cysts are present at birth and grow very slowly, usually becoming large enough to cause problems in the reproductive years. Therefore, removing them will solve the problem and nothing needed to avoid getting more.

Usually do not recur: Dermoid cysts or Teratomas are the most common type of germ cell tumor. Most are mature type (benign). They usually contain hair, teeth and skin mixed in a thick oily and sticky material, sometimes with a bad smell. They are usually remove to prevent complications eg rupture or torsion of the ovary and to make a diagnosis. They usually do not recur if surgically remove.