If I so much as huff on my skin (ok an exaggeration) I get funny red bruises, yet if I have a genuine knock, it's purple.
The red ones last twice as long as the purple.
Any ideas?
ferfew......it is a matter of degree of trauma on a thin and vulnerable skin as seen particularly in the elderly.
Minor trauma will lead to smaller blood vessels being damaged called petechia and a more robust trauma may lead to larger blood vessels being damaged producing a bruise.
There may be many causes of petechial hemorrhages, but trauma in the elderly is far away the commonest.