Why is my (white) neighbor's face purple?

One of my neighbors has some sort of condition that looks like a huge splotch of purple covers about half of his face. I’ve been swimming lately with him, and I don’t know him well enough to ask about it, nor can i imagine a scenario in which it’s any of my business (we’re on a “Hi, Howa ya doing?” basis) but I am curious. Is there a clear answer to this or is it possibly due to any number of causes? The purple part of his face appears to be slightly elevated, if that helps.

Sounds like port-wine birthmark:

See: Mikhail Gorbachev.

Has he had it as long as you’ve known him, or is it new?

I’ve only known him for about a year.

But it’s possible he’s always had this? Because then a birthmark seems likely. Whereas if it’s something that has emerged recently it’s obviously not a birthmark.

Entirely possible. He looks to be in his eighties.

This. I went to high school with a guy who, like the OP’s neighbor, had one that covered about half his face.

I had a high school teacher with something similar. Not very much of it on his face/neck, but one hand was pretty much completely covered in purple.

Perhaps, a survivor of a Wonka factory tour?

Many years ago, a friend of mine stayed at my house for a couple weeks. He performed cunnilingus on some random woman one night and a couple days later developed a weird infection on his face. It looked like someone had carefully placed a 1mm layer of purple playdo on half of his face. It was slightly shiny. He got something from the doctor for it but did not stay at my house long enough for me to see it heal. My wife nuked the sheets as soon as he left.

I’ve had one on my left cheek since I was born.

It’s roughly elliptical in shape with a length of about an inch along the major axis, half that along the minor axis. I was occasionally asked about it when I was a kid/teenager, but I don’t remember anyone mentioning it in the past 20 years and I keep on forgetting it’s there. It never bothered me, other kids always seemed more curious than mocking.

If anything, it has become slightly paler since I was a baby.

Avant-Garde tattoo.

If it’s most of his face, he could have a problem with high blood pressure and alcoholism.

The body is a weird thing. When I was younger, my hair was a dark chestnut, all over my body. Except for a foot-long strip of white hair along my left shin, like a blaze on a horse. My uncle told me that when he was my age he had the same thing, and eventually the hair all fell out; and sure enough, that happened with me. Long before I started losing the hair on my head.