Answer by  
                                                                                          rosieposey78 (1304)
                                                            
                          
                          
                                                          The cause of a dermoid cyst is due to skin structures that became trapped during fetal development. These skin structures continue to grow outside and/or inside which causes the cyst to grow larger as the structures also grow larger. Sebaceous glands or hair follicles can also form part of these cysts.