This is a question of development. There are two most common sternal malformations. The first one is called "chicken breast" in medicine. The sternum protrudes outward, and the whole chest looks like a chicken's chest, so it is called chicken breast. The second kind is called "funnel chest" in medicine. The sternum is depressed inward and the whole chest is funnel-shaped, so it is called funnel chest. If these two kinds of chest deformities are serious,