"Blushing is something I don't have control over. I can blush at the drop of a hat, whether I am embarrassed, happy, sad, angry or not," Bill Leverich of Kansas wrote in an e-mail to ABCNews.com.
Leverich said it hadn't affected his personal life, but he does wonder what it does to his career.
"I wonder if they think I am lying to them or just uncomfortable talking with them, when 99 percent of the time I have nothing to be embarrassed or concerned about," wrote Leverich. "I try to see it as a positive in that I feel it makes others feel they may be in control, while I in fact am, but it can still cause me to lose some focus when I can feel my face turning red."
Mark Leary, a professor of psychology and neuroscience at Duke University who studies blushing, says the reaction has more to do with being watched than with guilt.
"It tends to be embarrassment. But the more broad reason is that people blush when they receive undesired social attention," said Leary, adding that anyone can have the blood rush to their face in the spotlight -- it just shows up more in people with fairer skin.
Unfortunately for the blushers, Leary said it's almost impossible to stop the red hue once it starts. "You can't do it by force of will," he said. "There is a suggestion in one study that at the moment it is happening, try to blush as hard as you can."
Frequent blushers may have more hope trying to prevent a bright red hue than stem it once it starts, said Dr. Doris Day, a New York dermatologist.
"Blushing happens usually because of some sort of a stress trigger. You might not feel the stress anymore but at some point in your life you felt a trigger," she said.
Day says some drugs, including histamines and beta blockers, have been shown to reduce redness in the face either from social triggers or from heat, spicy foods and alcohol.
"Sometimes taking beta blockers when it's going to be a stressful situation can help," said Day. "Histamines help more for the physical triggers."
However, Day said using histamines on a short-term basis will not help a red face: They must be taken over time in consultation with a doctor.
Sweating isn't exactly a bodily function one can control, but the vast majority of people have the luxury of sweating when everyone else in the same hot car, on the same basketball team or in the same classroom is just as hot as they are.
That's not so for the 2 to 3 percent of people with unpredictable, uncontrollable sweating, or hyperhidrosis.
"Ever since I was in elementary school, I'd say probably second grade, I remember being in class and my hands just sweating as I worked, having my hand on a paper, and the paper being saturated from my hands sweating so much," Wendy Burke told ABC News' "Good Morning America" in 2004. "So, I mean, it's really been something I've lived with almost all my life."
Burke said at first adults didn't believe her, and doctors did not take her seriously. They said, 'Oh, you're just clammy.' Everybody blew me off."
Dr. David Pariser, current secretary of the International Hyperhidrosis Society, told "Good Morning America" that many hyperhidrosis patients suffer socially and practically from the condition.