Teratomas are embryonal tumors that look like little "monsters". They are composed of elements from the three germ layers of embryos, that is, the endoderm, the mesoderm, and the ectoderm. This is what causes teratomas to contain different types of tissues, including hair, teeth, bones, cartilages, etc.
There exist two different types of teratomas. On the one hand, mature teratomas, which are benign tumors; on the other, immature teratomas, which are malignant or cancerous tumors. The good news is that the benign type is the most frequent one, and it is also known as dermoid cyst or mature ovarian teratoma.