Strategic Air & Space Museum’s 60 Days of Science – 60 Days of Science Myths #4 Blood in your veins is blue and turns red when exposed to air. It is a common held belief that human blood is blue until it is oxygenated by air from the lungs, or until exposed to the air outside the body. This idea most likely comes from two primary sources; first, the plethora of human biology illustrations that show arteries as red and veins as blue, and second, direct observation of veins through the inner wrist, the side of the foot, and other parts of the body. A third source of the misinformation, as with many misconceptions, simply comes from individuals passing it on to others as fact. Human blood is red because the hemoglobin protein that it is composed of is colored red. The hemoglobin is red because of the way light interacts with the iron molecules within the cells. Regardless of the location within the body, all healthy blood is red, although oxygenated blood is brighter in color, and deoxygenated blood is darker. With these facts in mind, comes the legitimate question; why do veins appear blue under the skin? The apparent blue color comes from the absorption of longer, lower-­‐energy wavelengths (like the color red) as the light passes through the skin and fatty tissue of the body. The only wavelengths that remain after penetrating the body and reflecting back into our eyes are the more energetic shorter wavelengths associated with the color blue. Here is a fun and related way to demonstrate this phenomenon. Fill a translucent white straw with a red drink like Kool-­‐Aid® or fruit punch. Carefully fold over the ends, and crimp shut with rubberbands. You will already notice some color change in the red liquid. Place your makeshift vein on the bottom of a bowl, and slowly pour on top a very thin layer of milk. When viewing your “blood filled” vein, it will appear to be colored a washed-­‐out blue. http:// http://chemistry.about.com/od/lecturenoteslab1/a/Why-­‐Veins-­‐Look-­‐Blue.htm http://www.nlb.gov.sg/blogs/ask/children/81 © 2014 Michael Sibbernsen