First lady Michelle Obama today flatly denied speculation that the president dyes his hair.
"It's lighting," she said to television viewers this morning. "No, I think that if he had known he would be president, he would have started dying his hair, like, 10 years ago."
Mrs. Obama said the president is not vain about his appearance.
"I wish that he would focus more on a different color suit, a new shirt," she said on the "Today" show. "Sasha and I, Malia, we cheer when he puts on a bright-colored shirt."
Obama began to show a sprinkling of gray in first official portrait, unveiled in 2008. But various photographs of the president over the past year or so seemed alternatively to show no gray or a smattering, raising speculation about possibly using dye.
"The gray is coming quick," he reportedly said just before his inauguration in 2009 at age 47. "By the time I'm sworn in, I will look the part."
President Reagan famously denied that he ever dyed his lustrous locks. President Clinton's hair grew ever-whiter during his two terms. And President Bush visibly aged from his first inaugural through the trauma of 9/11 and two unpopular wars.
Most medical experts say that genetics plays the largest role in determining when a person goes gray, but new research seems to back the old wive's tale that stress, indeed, can turn the head white, or at least gray. Some researchers say persistent mental or physical stress that lasts two or more years can cause premature aging of the hair.
The French say Marie Antoinette turned gray overnight when she awaited her fate with the guillotine -- a legend that at least one doctor said likely had a medical explanation. Anxiety may have made her hair temporarily fall out in a condition called telogen effluvium, leaving the pale villus -- or "baby hair" -- behind.
Dr. Anthony Gaspari said Obama's hint of gray may not be related to stress.
"In Obama it looks genetic," he told ABCNews.com.
"There's a common garden-variety graying of hair that is a gradual process from the death of cells on the hair follicle," Gaspari, a dermatologist from the University of Maryland Medical Center.
But one researcher who has studied gray hair and its causes claims Americans are going gray five years earlier than they did in 1970 -- and probably because of stress.
"Basically, people gray as they grow older," said osteopath Tyler Cymet, vice president of medical education at the American Association of Colleges of Osteopathic Medicine who practices at Northwest Hospital outside Baltimore. And Obama is right on target, age-wise.
The average white male goes about 30 percent gray at the age of 34, "give or take nine years," Cymet told ABCNews.com.
African-Americans hit the 30 percent gray mark at 44 years old, plus or minus 10 years.
After the head turns 30 percent gray, it is another two to seven years until a person is fully gray. About 50 percent of all people are graying by 50. For Obama, at 49, that's just around the corner.
White Mother, Black Father Affect Obama's Hair
"With President Obama having a white mother and an African-American father, he would fit in the middle of the two groups," Cymet said.
Hair color is determined genetically by the amount of melanin pigments produced by stem cells called melaocytes. There are two types of pigments: eumelanin (dark brown or black) and phaeomelanin (yellow blond to red).
At the end of the active phase of hair growth, the building blocks of hair in the follicle -- kerotincytes and melanocytes -- die. As you age, fewer melanocytes are replaced. New hairs growing from these follicles are depigmented and appear gray or white.
Stress can affect how quickly hair is shed, and the faster it regrows, the more quickly the pigment breaks down.
Cymet explains that hair growth comes in three phases -- growth, resting and breakdown in six-year cycles -- about seven to 15 cycles in a lifetime. When a person becomes highly stressed in the growth stage, that cycle could be reduced to two years.
"You have seven to 15 cycles of hair growth before you lose the color," Cymet said. "If you speed it up and go through the growth phase quickly by not sleeping or eating or high stress levels, like being president, it happens more quickly."
A variety of physical conditions can also cause the hair to whiten or fall out: autoimmune disorders, hypo- and hyperthyroidism and alopecia, rare genetic disorders, including piebaldism and Waardenburg syndrome, and even a vitamin B deficiency.
"But I don't think that's what our highly stressed leaders have," Cymet said.
Charles Figley, a psychologist who specializes in traumatic stress at Tulane University, told ABCNews.com that he's not worried that Obama's first white hairs signal health issues, but he does confirm that the presidency can take its toll.
"With excessive stress over time -- the four-year hot seat of the presidency -- cells can break down," he said.
Psychological stress is more apt to take a toll on a person's physical health than their hair color, according to Figley, yet the myths persist.
Figley does not dismiss the notion that this kind of stress could hasten the graying process.
"The physical environment can affect the brain, which affects our immune system," Figley said. "But stress is difficult to evaluate."
And presidents handle their stress differently. Obama is not a known worrier and seems to release his stress on the basketball court or in his daily gym workouts.
"This guy [Obama] is a well-balanced person who had to think on his feet," said Figley. "He hasn't had any handlers until more recently, and he's been forced to know how to address and manage stress."
And, said Figley, the president-elect is an optimist, a quality that studies show correlate with a long life expectancy.
"We're beginning to think that optimism is part of a very important trait -- ego resiliency that has been found to be highly correlated with positive effects," he said. "People can have terrible adversity, yet a buoyant attitude and their positive outlook doesn't change."
But hair stylists like Lee Kostu, who has seen hundreds of graying heads at Hair It Is salon in Robbinsville, N.J., is not totally convinced that it's all genetic, especially for those whose lives are stressful.
"Sometimes I see a little gray in a client and then they come back for the next cut and bam -- they're all white," he said.