Superman has complete immunity towards any conventional form of physical harm.

His skin, eyes & hair are impenetrably; object will bounce of or just bend and break on contact. He also has immunity to almost all forms of ailments, including extreme force and extremely high temperatures. This ability includes the immunity to most known physical and mental diseases, viruses and toxins.

This power is due to his superhumanly dense cellular and anatomical structure as well as his radiating bio-electrical aura. The aura acts as an invisible "force field" radiating within a few millimeters from his skin, allowing some protection to his tightly worn clothing as well.

Green Kryptonite negates this ability and makes Superman vulnerable.