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.
"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).