Why a healing wound / developing scar keeps cycling in appearance?

April 21, 2022 1:15 AM

I fell on a slippery tidal pool five weeks ago and cut approximately 2x2" of my knee up. The wound has since healed and what's left is what I'd assume is early scarring though it does have sensitivity to pressure, too, so maybe still late-stage bruising as well? Sometimes now when I look at my knee, it is very close to my normal skin color. Other times, it's quite a bit darker. There's not necessarily a pattern I've noticed as to why. I'm not worried about it, just curious about the scientific explanation.

I know scars can change color in the shower/with heat. That is not (exclusively, at least) what is happening. It's - to me, randomly - quite a bit more intense sometimes and then other times it's not nearly as noticeable and I don't see a clear link to my immediate environment, time of day, etc. Why is it so variable in appearance?

posted by vegartanipla to Science & Nature (2 answers total)

Best answer: My guess is that you’re looking at how dilated your capillaries are (more dilated, more dark blood visible through the thin skin of the healing scar), and that’s going to vary over the course of the day based on a whole lot of physiological factors (temperature, activity, caffeine, alcohol, stress) some of which are pretty inconspicuous to you.
posted by LizardBreath at 6:56 AM on April 21, 2022 [2 favorites]

Best answer: So, under the top layer, all of your skin is doing that variation all the time. The stratum corneum is the top layer of your epidermis. It is a layer of "dead" skin cells, which themselves do not grow but rise up from the lower layer. The stratum corneum changes the refractive properties of skin. That is, light bounces off of it more than the lower layers. In freshly healed areas of skin, you have not yet sufficiently built up the layers of cells to reflect light as your skin usually does. So the changes in capillary action are much more visible there.
posted by ewok_academy at 7:27 AM on April 21, 2022 [3 favorites]