Why do bruises (black and blue marks) turn yellow?

Don’t quote me on this, but I thought it was the increase in antibodies/white blood cells in the area. Puss, or whatever.

I’m probably the least qualified person to speak about this.

^ No. As your body breaks down the hemoglobin, the resultant bilirubin and biliverdin appear as greenish yellow.

It is the red blood cells degrading. A bruise is leaking of blood into the damaged tissues, and as the hemoglobin (red) degrades, the heme pigment also degrades, changing the color from purple to various other shades, like green and yellow. Bilirubin (the ultimate breakdown product) is a greenish-yellow color, so the degree of bleeding and timing of the degradation dictate what color your skin is at any given time. Eventually, the damaged tissue is healed, and the red blood cells are eaten up, leaving no visible mark.

“t is the hemoglobin in the red blood cells and the breakdown products of the hemoglobin that cause the coloration seen in bruises as they age. Although bruises may appear black eye, the blood is never really black, rather it is a dark purple and green. Most of the color seen in bruises is due to the biochemical breakdown of hemoglobin, the oxygen-carrying component of blood (white blood cells are removing the decayed blood products little by little). Different components of the blood have different colors, and these colors in turn lend color to the bruise. There are two major breakdown products that can lead to visible color in a bruise. These are a green pigment called biliverdin and a yellow-brown pigment called bilirubin. Bruises usually start out as a dark blue or crimson; fade to violet, green, and dark yellow; then turn a pale yellow; finally disappearing completely.”

From this site.

Ya see? What I say?

According to WebMD-
Blood leaks into tissues under the skin and causes the black-and-blue color. As bruises (contusions) heal, usually within 2 to 4 weeks, they often turn colors, including purplish black, reddish blue, or yellowish green.

But personally, I think it’s because they’re cowards.

@Grisaille: I do hope you mean pus.

@gailcalled Maybe. Maybe not.

You decide.

Milo here; It is definitely pus. All cats are not gray in the dark, (or grayish).

That’s right, Milo. But many British Shorthairs are grey in the dark, though.

Milo here: Brits. use “grey”; we use “gray. It’s humourous, don’t you think?

Rippingly so, old bean.