Everyone at some time has experienced a “black and blue” mark, which is actually a flat skin bruise. They can occur anywhere on your skin and at any age, although they’re much more common in older adults.
Very simply, they’re the result of bleeding in the skin from damaged or broken blood vessels, which usually comes from blunt trauma, like a fall or just from knocking into things. Usually, the damage is to capillaries or tiny veins, which we call venules, in the dermis, the second layer of skin, and much less commonly it’s from veins in the fat in the third layer of skin, called the subcutis.
When blood vessels are damaged, blood leaks out from them into the surrounding tissues, called the interstitial spaces, and causes the flat black and blue spots which are just collections of free blood and have fancy names like “purpura” and “hematoma”. Usually, there is no tearing or breaking of other skin tissues. And the reason that you don’t “bleed” is because the upper layer of skin, the epidermis, hasn’t been broken, so the free blood can’t get out. The colors go from black and blue, to purple, rust and yellow, and sometimes, the area of the discoloration spreads down the body in the direction of gravity, especially on the face and legs.
As we get older, our skin becomes thinner and the capillary walls become more brittle, so it’s very common for people in their 60’s and older to experience black and blue spots from literally pinching their skin or even just rolling over on their arm or hand during sleep. That’s called “pinch purpura” or less kindly, “senile purpura.”
I even have a very wealthy patient who keeps getting frequent black and blue spots on her forearms and wrists from her very heavy expensive jewelry hitting against her skin.
Now that’s what I call a “high class” problem!
You don’t have to treat these black and blue spots because the blood is reabsorbed into the body, and heals on the inside. But, many people believe that frequent application of topical arnica preparations may actually speed the disappearance of the black and blue spot.
Black and blue spots may be unattractive, but they’re not dangerous.