Viscosity is the resistance of a liquid to movement. Think water versus honey, honey being very viscous. Turns out a number of things can make the blood flowing through our bodies more or less viscous.
Some possible causes of increased blood viscosity are dehydration , psychological stress , cold temperatures , heat stroke , increased hematocrit (serum red blood cell) levels , hyperglycemia , increased triglycerides and chylomicrons in the blood , and perhaps exposure to air pollution  and tobacco smoke . Continue reading