The Blush

The Blush
Wiki: “Blushing is the reddening of a person’s face due to psychological reasons. It is normally involuntary and triggered by emotional stress, such as that associated with embarrassment, anger, or romantic stimulation.”
Here’s another from How To: “It is normally triggered by a social phobia such as shyness or embarrassment.”
According to research doctors blushing is governed by the same system that activates your flight or fight response: the sympathetic nervous system.
We’re not here to do medical research. We’re here to write better more believable characters. We should not tell the reader why the none-view point character blushed, we’re here to show why. Tough task. On the other hand, misinterpreting the blush (as an unreliable narrator or POV character should or would do) can lead to plot twists, black moments, comedy, etc.
Example: They were just friends and he wants to see if she’s romantically inclined. He says, “if you were my gal, I’d (insert something kindly or heroic).”
She blushes and tries to change the subject. BTW, men blush too, so this can be reversed.
Back to our hero. He assumes she’s romantically inclined after observing the blush and proceeds to get chummier. But she could be angry or embarrassed. There are other minor explanations for blushing which I’ll leave to the student of human nature, but I’ll suggest for the purpose of fiction to stay on main paths unless your hero or heroine is a doctor/researcher type.
Or, if in her POV, she could show internal thought to explain her reaction or perhaps she doesn’t fully understand her reaction since blushing is an involuntary response. It is possible, if she were angry, that it was a combination of symptoms. You see what I’m saying to all you detective Colombos out there? Don’t make it easy unless you have reached that point in their arcs where truth telling was a complete necessity. Hey, they’re in love, secretly, and it was about time they both said the truth and confirmed it with a kiss.
Trick question: Why do Victorian novels feature the blush and modern stories underutilize it? Note that since the blush is involuntary, and humans have not changed the blush is still alive and well and ready to be used as an arrow in your quiver of skills. I love you all. Now, I’m blushing.