An incision is made to access the surgical site. Blood vessels may be clamped or cauterized to prevent bleeding, and retractors may be used to expose the site or keep the incision open. The approach to the surgical site may involve several layers of incision and dissection, as in abdominal surgery, where the incision must traverse skin, subcutaneous tissue, three layers of muscle and then peritoneum. In certain cases, bone may be cut to further access the interior of the body; for example, cutting the skull for brain surgery or cutting the sternum for thoracic (chest) surgery to open up the rib cage. Whilst in surgery health and safety is used to prevent infection or further spreading of the disease. The surgeon will remove hair from the face and eyes, using a head hat. Hands, wrists and forearms are washed thoroughly to prevent germs getting into the operated body, then gloves are placed onto the hands. A PVC apron will be worn at all times, to stop any contamination. A yellow substance – typically an antiseptic iodine solution – is lighly coated onto the located area of the patient’s body that will be performed on, this stops germs and disease infecting areas of the body, whilst the patient is being cut into.