I play with my cat a lot, which unfortunately means I get scratched and bitten all over my hands and arms. Usually they’re not serious, not even breaking the skin, but they do puff up to little red and white-ish lines. What causes this?
(It’s not an allergic reaction to my cat or anything - it happens to my skin whenever I get scratched on anything.)
The main cause is the release of histamine from a type of cell known as the mast cell, which can be found throughout the body. Histamine causes small arteries and veins to dilate, which results in increased amounts of blood hanging around the injury site. This increased blood is what makes the skin swell. Mast cells can release their histamine in response to physical injury (as in your case), as part of an allergic response, or through various other triggers.
Possible slight addition (just because I read something about this the other day in a book I’m reading on blood-drinking animals), in addition to dilation the reaction to injury also makes the blood vessels in the area more porous, allowing white blood cells greater access to the injured area.
Or do I misremember this little tidbit?
You’re right. I forgot to mention the part about the edema.