As more carboxyhemoglobin is formed, the amount of oxygen carried to the cells and organs in the body decreases. Carbon monoxide starves the blood of oxygen, literally causing the body to suffocate from the inside out. When the carboxyhemoglobin concentration reaches a certain level, people get nauseous, become unconscious, and ultimately die. How quickly symptoms appear depends upon the concentration, or parts per million (ppm) of carbon monoxide in the air and the duration of exposure.