# What color is human blood? **URL:** \ **Category:** Factual Questions\ **Created:** [April 6, 2001, 11:13pm UTC](https://boards.straightdope.com/t/what-color-is-human-blood/61098 "2001-04-06T23:13:08Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![KaBone](https://avatars.discourse-cdn.com/v4/letter/k/a87d85/32.png) [@KaBone](https://boards.straightdope.com/u/KaBone)\ **Post date:** [April 6, 2001, 11:13pm UTC](https://boards.straightdope.com/t/what-color-is-human-blood/61098/1 "2001-04-06T23:13:08Z")
What color is human blood, red or blue? I’ve heard before that blood is blue until it comes in contact with air, upon which it turns red. That statement is backed up by the fact the veins in your wrist appear blue, and a person turns blue when they asphyxiate. However, when someone gives blood, or blood is drawn from the arm it’s always dark red. The vessels used to draw blood and the bag used for donated blood is evacuated of air before use; so wouldn’t the blood be blue? That in conjunction with the fact I don’t know of anyone who has seen blue blood is the causes of my confusion. Enlighten us, Cecil. What color is blood? - CK ---
**Author:** ![Arjuna34](https://avatars.discourse-cdn.com/v4/letter/a/eb8c5e/32.png) [@Arjuna34](https://boards.straightdope.com/u/Arjuna34)\ **Post date:** [April 6, 2001, 11:18pm UTC](https://boards.straightdope.com/t/what-color-is-human-blood/61098/2 "2001-04-06T23:18:52Z")
Welcome to the SDMB, **KaBone**! Here’s the Mailbag answer to your question, answered by one of Cecil’s minions: [If blood is red why do your veins look blue?](http://www.straightdope.com/mailbag/mbloodrd.html) Many answers can be found using the [SDMB archive search page](http://www.straightdope.com/columns/index.html). Arjuna34 ---
**Author:** ![Gunslinger](https://avatars.discourse-cdn.com/v4/letter/g/4491bb/32.png) [@Gunslinger](https://boards.straightdope.com/u/Gunslinger)\ **Post date:** [April 7, 2001, 12:34am UTC](https://boards.straightdope.com/t/what-color-is-human-blood/61098/3 "2001-04-07T00:34:01Z")
Bright red when oxygenated, dark purple when not. ---
**Author:** ![JerseyDiamond](https://avatars.discourse-cdn.com/v4/letter/j/8491ac/32.png) [@JerseyDiamond](https://boards.straightdope.com/u/JerseyDiamond)\ **Post date:** [April 7, 2001, 3:25am UTC](https://boards.straightdope.com/t/what-color-is-human-blood/61098/4 "2001-04-07T03:25:51Z")
The red color of blood comes from the hemoglobin in the red blood cells. When oxygen is released it is bright red, when oxygen is taken away it darkens. I work in a lab and draw many tubes of blood. Blood is never ever blue. I use vacuum tubes in which the blood is not exposed to air, and I have had samples that were almost a glowing red to a maroon/burgandy color. From what I hear, veins are a whitish color. What determines the color of veins depends on skin pigment, the colors of light blood absorbs, and oxygenation of the blood. When there is not enough oxygen in the blood, skin has a bluish coloing to it. Arterial blood is\>\>\> where oxygen and nutients are taken to the tissues and venous blood is \>\>\> carbon dioxide and metabolic by products are transported for excretion. Sorry for rambeling. ---
**Author:** ![berdollos](https://avatars.discourse-cdn.com/v4/letter/b/ed8c4c/32.png) [@berdollos](https://boards.straightdope.com/u/berdollos)\ **Post date:** [April 7, 2001, 3:36am UTC](https://boards.straightdope.com/t/what-color-is-human-blood/61098/5 "2001-04-07T03:36:12Z")
I saw a puddle of human blood once. The surface had been oxidized and was a dark red or dark purple’ when it was being mopped up, most of it under the surface was red.crayfish blood is green - from its copper source. Human blood is red from the iron in hemoglobin.