I banged the side of my leg above and slightly to the fore of the lateral malleolus pretty hard on Monday. The spot hurts when I touch it, but there’s no bruise. Why is that?
Bruises occur when you break blood vessels. If you just banged up a muscle, you may not have done that. Hence, no bruise.
It’s also possible that it may take a day or two to show up.
Zombies don’t bruise. Just sayin’ . . .
The bruise may be too far beneath the surface to be visible.
I used to do a lot of martial arts. I was regularly confounded by what sorts of things would result and bruises, and which wouldn’t. Very often I’d know I took a hard shot somewhere, and it would hurt after, but no bruise. But then I’d have I nice purple handprint where someone apparently grabbed me - that I didn’t recall and that didn’t hurt. No clear rhyme or reason I could tell.
Same applied to simple life’s bumps. Walk into a coffee table - nothing. Bump iyour shoulder, huge bruise.
I used to bruise when I was a kid, but don’t now. Not sure why that changed.
Bad Muffin, bad! 
Sometimes if I have REALLY bruised myself, it takes a while to show up, sometimes long enough that it doesn’t really hurt by the time you can see it. Everyone says “OMG! That must HURT?” and I’m thinking “A week ago, yes. Now, not so much…”
How do you bruise a crystalline structure? Scratch it maybe, but bruise?
Sometimes it takes a few days for bruises to show up. Way back in the day when I played football, games were on Saturdays, and bruises would mysteriously show up Monday, Tuesday or Wednesday depending on the area, how hard the impact was, and if there was padding there.
Hey, Quartz, come over here and let me see. I’m a doctor you know, sez so right in my user name. OK, lie back on this exam table and stretch out that leg. Does it hurt when I do this? Mmhmm. How about this? Mmmmhmmm.
WHACK!
There, you should have a bruise shortly. That will be $7,000. Please pay the receptionist on the way out.
My mom got hit by a hockey puck on her shoulder a few months ago. She was fine but she was surprised she didn’t get a bruise right away. I told her to wait a few days. Three days later she sends me a picture of an impressive technicolor bruise. She said it didn’t even hurt anymore but looked terrible.
My bruises tend to show up sooner rather than later. I wonder if it’s because I have very fair skin- like one step above albino fair.
" 'Cause I’m a karate man! And a karate man bruises on the inside! " - Billy Ray Valentine
You guys ever have those bruises that, not only turn up later, but in a different place? I remember on time I fell really hard on my butt/hip, shortly before going to bed. Well, I sleep on my stomach, and I was surprised later on to develop an impressive bruise on the FRONT/inside of my leg/pelvis. And it was one of those that lingers and changes all the colors from purple through green and yellow. That was weird!
Then we’ll need to re-animate this thread in another five years and check again.
Hematoma = super bruise.
The blood can move around within tissue planes. You had blood leak into subcutaneous tissues- it moved to your front side as you lay on your stomach.
Still no bruise but the area is visibly swollen.
Probably a bruise or hematoma within the muscle itself.
Most visible bruises are due to rupture of capillaries and small vessels in the skin. The bruise is a small collection of blood (and later) blood products in the subcutaneous tissues. It’s close enough to to the skin surface to be visible.
If the bleeding is deep, you might not see a bruise, unless blood finds its way (moving along tissue planes) to the subcutaneous tissues.
The weird colors are due to conversion and breakdown of hemoglobin in the leaked blood.
Or if you hit bone, you may have a “bruise” just under the periosteum, the “skin” of the bone.
And this has now happened to me: I’ve just taken off my shoe to find there’s now a significant bruise mark the length and width of my forefinger on the outside of my ankle half an inch below the top of the shoe, but the painful bit - and there’s still a definite lump - is well above that - perhaps four inches above.
Bodies are weird.
I had a similar one last sumer - I was walking through a parking lot, closely behind the cars to stay out of traffic. A truck had a trailer hitch, and I barked my shin right into it. Amazing how much force you have just swinging your leg to walk!
It was getting better until I went on a hard bike ride a week later, after which it swelled up and drained down to the ankle. Got so I could hardly walk w/o a cane. I had had a trimalleolar fracture w/ ORIF of that ankle less than 6 months earlier. When it didn’t get better, I went to my ortho, wondering if it was broken, if I was going to toss off a blood clot, or what… X-ray was negative. He said they couldn’t even drain anything, as it would have been the consistency of jelly. Just had to wait A LONG TIME for it to be reabsorbed.