Few harbingers of old age are clearer than the sight of gray hair. As we grow older, black, brown, blonde or red strands lose their youthful hue. Although this may seem like a permanent change, new research reveals that the graying process can be undone—at least temporarily.
Hints that gray hairs could spontaneously regain color have existed as isolated case studies within the scientific literature for decades. In one 1972 paper, the late dermatologist Stanley Comaish reported an encounter with a 38-year-old man who had what he described as a “most unusual feature.” Although the vast majority of the individual’s hairs were either all black or all white, three strands were light near the ends but dark near the roots. This signaled a reversal in the normal graying process, which begins at the root.
In a study published today in eLife, a group of researchers provide the most robust evidence of this phenomenon to date in hair from around a dozen people of various ages, ethnicities and sexes. It also aligns patterns of graying and reversal to periods of stress, which implies that this aging-related process is closely associated with our psychological well-being.
These findings suggest “that there is a window of opportunity during which graying is probably much more reversible than had been thought for a long time,” says study co-author Ralf Paus, a dermatologist at the University of Miami.
Around four years ago Martin Picard, a mitochondrial psychobiologist at Columbia University, was pondering the way our cells grow old in a multistep manner in which some of them begin to show signs of aging at much earlier time points than others. This patchwork process, he realized, was clearly visible on our head, where our hairs do not all turn gray at the same time. “It seemed like the hair, in a way, recapitulated what we know happens at the cellular level,” Picard says. “Maybe there’s something to learn there. Maybe the hairs that turn white first are the more vulnerable or least resilient.”
While discussing these ideas with his partner, Picard mentioned something in passing: if one could find a hair that was only partially gray—and then calculate how fast that hair was growing—it might be possible to pinpoint the period in which the hair began aging and thus ask the question of what happened in the individual’s life to trigger this change. “I was thinking about this almost as a fictive idea,” Picard recalls. Unexpectedly, however, his partner turned to him and said she had seen such two-colored hairs on her head. “She went to the bathroom and actually plucked a couple—that’s when this project started,” he says.
Picard and his team began searching for others with two-colored hairs through local ads, on social media and by word of mouth. Eventually, they were able to find 14 people—men and women ranging from nine to 65 years old with various ethnic backgrounds (although the majority were white). Those individuals provided both single- and two-colored hair strands from different parts of the body, including the scalp, face and pubic area.
The researchers then developed a technique to digitize and quantify the subtle changes in color, which they dubbed hair pigmentation patterns, along each strand. These patterns revealed something surprising: In 10 of these participants, who were between age nine and 39, some graying hairs regained color. The team also found that this occurred not just on the head but in other bodily regions as well. “When we saw this in pubic hair, we thought, ‘Okay, this is real,’” Picard says. “This happens not just in one person or on the head but across the whole body.” He adds that because the reversibility only appeared in some hair follicles, however, it is likely limited to specific periods when changes are still able to occur.
Most people start noticing their first gray hairs in their 30s—although some may find them in their late 20s.This period, when graying has just begun, is probably when the process is most reversible, according to Paus. In those with a full head of gray hair, most of the strands have presumably reached a “point of no return,” but the possibility remains that some hair follicles may still be malleable to change, he says.
“What was most remarkable was the fact that they were able to show convincingly that, at the individual hair level, graying is actually reversible,“ says Matt Kaeberlein, a biogerontologist at the University of Washington, who was one of the editors of the new paper but was not involved in the work. “What we’re learning is that, not just in hair but in a variety of tissues, the biological changes that happen with age are, in many cases, reversible—this is a nice example of that.”
The team also investigated the association between hair graying and psychological stress because prior research hinted that such factors may accelerate the hair’s aging process. Anecdotes of such a connection are also visible throughout history: according to legend, the hair of Marie Antoinette, the 18th-century queen of France, turned white overnight just before her execution at the guillotine.
In a small subset of participants, the researchers pinpointed segments in single hairs where color changes occurred in the pigmentation patterns. Then they calculated the times when the change happened using the known average growth rate of human hair: approximately one centimeter per month. These participants also provided a history of the most stressful events they had experienced over the course of a year.
This analysis revealed that the times when graying or reversal occurred corresponded to periods of significant stress or relaxation. In one individual, a 35-year-old man with auburn hair, five strands of hair underwent graying reversal during the same time span, which coincided with a two-week vacation. Another subject, a 30-year-old woman with black hair, had one strand that contained a white segment that corresponded to two months during which she underwent marital separation and relocation—her highest-stress period in the year.
Eva Peters, a psychoneuroimmunologist at the University Hospital of Giessen and Marburg in Germany, who was not involved in this work, says that this is a “very creative and well-conceptualized study.” But, she adds, because the number of cases the researchers were able to look at was relatively small—particularly in the stress-related portion of the study—further research is needed to confirm these findings.
For now, the next step is to look more carefully at the link between stress and graying. Picard, Paus and their colleagues are currently putting together a grant to conduct another study that would examine changes in hair and stress levels prospectively—which means tracking participants over a specified period of time rather than asking them to recall life events from the past.
Eventually, Picard says, one could envision hair as a powerful tool to assess the effects of earlier life events on aging—because, much like the rings of a tree, hair provides a kind of physical record of elapsed events. “It’s pretty clear that the hair encodes part of your biological history in some way,” he says. “Hair grows out of the body, and then it crystallizes into this hard, stable [structure] that holds the memory of your past.”
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