The severity of the effects on organisms, especially human males, of histamine and serotonin biochemical interactions - and their subsequent behaviors - has been vastly underestimated in the scientific community. Humans, like all life, are sensitive to their environment. Mentally ill or unstable individuals can be triggered into impulsive and violent activities from spikes in serum serotonin. Human serum histamine level is directly proportional to environmental allergen or pollen levels, but serum serotonin level is inversely proportional to serum histamine levels with human males having 52% more serotonin than females. Data show an association between the dates of violent acts, especially male single shooter mass shootings in the United States, and the dates of dramatic decreases in pollen levels thus indicating pollen and serum histamine level drops as a possible precursor or triggering relationship. This knowledge can be used as a potential predictor for law enforcement and medical agencies for a given city or region. Mental health professionals would be advised to lower serotonin boosting meds and even supplement antihistamine and sedative medications to male patients in the timeframes of March through June, for spring tree pollens especially juniper tree pollen, and from September through November, for fall ragweed weed pollen.