# What exactly is a bruise **URL:** \ **Category:** Factual Questions\ **Created:** [July 28, 2004, 8:42pm UTC](https://boards.straightdope.com/t/what-exactly-is-a-bruise/257321 "2004-07-28T20:42:46Z")\ **Posts on this page:** 12\ **Page:** 1
**Author:** ![bummerboy](https://avatars.discourse-cdn.com/v4/letter/b/7c8e57/32.png) [@bummerboy](https://boards.straightdope.com/u/bummerboy)\ **Post date:** [July 28, 2004, 8:42pm UTC](https://boards.straightdope.com/t/what-exactly-is-a-bruise/257321/1 "2004-07-28T20:42:46Z")
I’ve always wondered what is a bruise, why do they hurt when you put pressure on them, why are they yellow, green, blue, a dullish gray, brown, and why do some have little red spots on them. I just crashed on my dirtbike and have 3 big ones on my legs, which brought me to this question. Also, why are they called black-and-blue marks? ---
**Author:** ![indecisive1](https://avatars.discourse-cdn.com/v4/letter/i/41988e/32.png) [@indecisive1](https://boards.straightdope.com/u/indecisive1)\ **Post date:** [July 28, 2004, 8:47pm UTC](https://boards.straightdope.com/t/what-exactly-is-a-bruise/257321/2 "2004-07-28T20:47:25Z")
oh boy… bummer, bummerboy! ---
**Author:** ![indecisive1](https://avatars.discourse-cdn.com/v4/letter/i/41988e/32.png) [@indecisive1](https://boards.straightdope.com/u/indecisive1)\ **Post date:** [July 28, 2004, 8:59pm UTC](https://boards.straightdope.com/t/what-exactly-is-a-bruise/257321/3 "2004-07-28T20:59:35Z")
Sorry, I had to get my dumb joke in before someone beat me to it. A bruise is blood that has leaked out of your blood vessels that is trapped under your skin. I’ll leave the rest for our many medical experts. P.S. I really am sorry you wiped out and got hurt. ---
**Author:** ![silk1976](https://avatars.discourse-cdn.com/v4/letter/s/8edcca/32.png) [@silk1976](https://boards.straightdope.com/u/silk1976)\ **Post date:** [July 29, 2004, 2:52am UTC](https://boards.straightdope.com/t/what-exactly-is-a-bruise/257321/4 "2004-07-29T02:52:31Z")
I just had my wisdom teeth taken out a few weeks ago, and when I went for a followup visit, I had yellowish bruises on my cheeks. I’ve noticed that many times, a bruise eventually turns yellow before it completely goes away. The oral surgeon said that it was yellowish because that was the iron in the blood oxidizing, ie. rusting. I’m not a doctor, and thats not a complete answer, but I found it interesting. ---
**Author:** ![Demo](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/demo/32/8472_2.png) [@Demo](https://boards.straightdope.com/u/Demo)\ **Post date:** [July 29, 2004, 5:42am UTC](https://boards.straightdope.com/t/what-exactly-is-a-bruise/257321/5 "2004-07-29T05:42:45Z")
There’s really not much more to it than **silk1976** said. Bruises form when capillaries(tiny blood vessels) under the skin are broken from some sort of trauma and release blood into the surrounding tissue. Depending on your original skin tone the bruise can look different colors. As the blood is metabolized, broken down and whisked away by your lymph system the pooled blood, plasma and broken down blood proteins change colors. Oh, as to the pain, that is from the infiltrated blood solids and liquids exerting pressure on the surrounding tissue. ---
**Author:** ![bizzwire](https://avatars.discourse-cdn.com/v4/letter/b/958977/32.png) [@bizzwire](https://boards.straightdope.com/u/bizzwire)\ **Post date:** [July 29, 2004, 5:49am UTC](https://boards.straightdope.com/t/what-exactly-is-a-bruise/257321/6 "2004-07-29T05:49:19Z")
Your doctor is kinda sorta right; the change in color is not caused by oxidation of the iron, but by the breakdown of the “heme” portion of the hemoglobin in the released blood. As this porphyrin molecule breaks down, it’s absorption spectrum changes from being red to green to yellow. ---
**Author:** ![PookahMacPhellimey](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pookahmacphellimey/32/3175_2.png) [@PookahMacPhellimey](https://boards.straightdope.com/u/PookahMacPhellimey)\ **Post date:** [July 29, 2004, 10:13am UTC](https://boards.straightdope.com/t/what-exactly-is-a-bruise/257321/7 "2004-07-29T10:13:15Z")
So why do some people bruise so much easier than others? I always have a few unexplained buises somewhere, some of them look quite bad and I never even noticed getting them. I suppose I just have weak cappilaries. Or can there be other reasons? ---
**Author:** ![Demo](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/demo/32/8472_2.png) [@Demo](https://boards.straightdope.com/u/Demo)\ **Post date:** [July 29, 2004, 3:40pm UTC](https://boards.straightdope.com/t/what-exactly-is-a-bruise/257321/8 "2004-07-29T15:40:20Z")
> [@PookahMacPhellimey](#): > > So why do some people bruise so much easier than others? I always have a few unexplained buises somewhere, some of them look quite bad and I never even noticed getting them. I suppose I just have weak cappilaries. Or can there be other reasons? I know some people just have more fragile vasculature, like you mentioned. This happens a lot in the elderly. People on blood thinners like heparin or coumadin are also more prone to bruising. ---
**Author:** ![GilaB](https://avatars.discourse-cdn.com/v4/letter/g/8e7dd6/32.png) [@GilaB](https://boards.straightdope.com/u/GilaB)\ **Post date:** [July 29, 2004, 4:27pm UTC](https://boards.straightdope.com/t/what-exactly-is-a-bruise/257321/9 "2004-07-29T16:27:22Z")
My tae kwon do teacher tells me that eventually my forearms (the major blocking surface) will stop bruising. Is this because eventually I’ll have blown out all of the capillaries in my arm, or do they heal and somehow become more damage resistant? If it’s that I’ll have blown out all of the surface capillaries, is that bad for me? ---
**Author:** ![racinchikki](https://avatars.discourse-cdn.com/v4/letter/r/eada6e/32.png) [@racinchikki](https://boards.straightdope.com/u/racinchikki)\ **Post date:** [July 29, 2004, 4:36pm UTC](https://boards.straightdope.com/t/what-exactly-is-a-bruise/257321/10 "2004-07-29T16:36:22Z")
> [@bummerboy](#): > > Also, why are they called black-and-blue marks? Um… because they are black and blue? At least when they are fresh. ---
**Author:** ![GilaB](https://avatars.discourse-cdn.com/v4/letter/g/8e7dd6/32.png) [@GilaB](https://boards.straightdope.com/u/GilaB)\ **Post date:** [July 29, 2004, 5:09pm UTC](https://boards.straightdope.com/t/what-exactly-is-a-bruise/257321/11 "2004-07-29T17:09:23Z")
Actually, when mine are fresh, they’re a kind of pleasant pale purple color (it’s almost pretty, except that it’s on my flesh, it hurts, and it’s definitely not my most flattering color :)) that darkens, eventually fades to brown, then to yellow. It never really gets to black or blue - dark purply-brown is the closest it gets to black, and I’m not sure where the blue comes from. I’m a pretty pale person, though, and maybe on people with a different skin color, it comes through as blue? ---
**Author:** ![racinchikki](https://avatars.discourse-cdn.com/v4/letter/r/eada6e/32.png) [@racinchikki](https://boards.straightdope.com/u/racinchikki)\ **Post date:** [July 29, 2004, 5:23pm UTC](https://boards.straightdope.com/t/what-exactly-is-a-bruise/257321/12 "2004-07-29T17:23:01Z")
I don’t know that it would do with paleness, per se. I am almost translucent, I am so pale. (To give you an idea: I cannot buy makeup in department stores, because the lightest mass-produced shade is far too dark for my skin.) And yet when I bruise, it is SPECTACULAR in its darkness and painful-looking-ness (although it doesn’t really hurt that bad). Black and blue and purple and AWFUL. I find big blue bruises on my legs sometimes and I have no idea what I’ve bumped into to cause them.