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.