There are many life threatening, as well as psychological, dangers due to the use of marijuana. Life threatening dangers include, cancer, breathing, immune system, asthma, driving ability, heart rate, blood pressure, and reproduction. The Psychological findings include, short term memory, attention span, "lasting effect", schizophrenia, withdrawal, and symptoms in newborns, and children. These certain dangers may be associated with the prolonged use of marijuana, and may cause permanent damage. Marijuana is known to contain more of some cancer causing agents than filtered tobacco cigarettes. People who smoke marijuana inhaled three times as much tar and retained one third more tar in their lungs than tobacco smokers. The carbon monoxide level in marijuana smokers was five times as high as tobacco smokers also. Compared to cigarette smokers, and non-cigarette smokers, people who smoke marijuana show reduced airway function. The loss of function was worse among people who smoked marijuana, than it was in people who smoked cigarettes. Marijuana smokers have a lesser ability to fight off infections and cancer. The cells in the lungs that breakdown and fight disease, were unable to destroy staphylococcus, or what might be known as strep throat. Also a lack in the ability to kill tumor cells was prevalent, as well as the inability to produce interleukins, and other cancer killing biochemical's. Another aspect of the dangers of marijuana is asthma. Some people are allergic to cannabis pollen, resulting in asthma, or inflammation of the nose. In a test that was given in Nebraska, 122 people were given skin tests for cannabis pollen, and other ragweed allergens. Forty-eight of the 122 tested positive for cannabis pollen, and of the forty eight who tested positive, twenty two experienced respiratory symptoms during the test period. Driving ability is also affected while using marijuana.