This article originally appeared on Tonic.
It's an oft repeated maxim that gray hair starts at the temples in men (see: Paulie Walnuts, Grandpa Munster). In fact, the word "temple" is derived from this assumption. The temporal bones and lobes of the brain underneath, located at roughly eye level on the sides of the head, get their name from the latin word, "tempus," meaning both time and the spot on the head, linking gray temples with aging and the passage of time.
In movies, tv and life, rubbing one's temples is a shorthand to indicate that you're stressed out. It's also the stock image for headache and migraine, the pain of which is often described as pressure at the temples, or feeling like one's mind is "in a vice." But research has thrown the link between gray hair and stress into question. While the onset of graying can be sped up slightly based on outside factors—UV exposure, smoking and exposure to other chemicals—the emergence of gray hair is about 90 percent controlled by genetics.
There have been many studies investigating the phenomenon of gray hair in general, as well as about the pattern of baldness, another sign of hair aging, but surprisingly few concern the pattern of hair graying. The question of why hair starts to go gray at the temples—or even whether it's true in the first place—still remains largely mysterious. "I'm not aware of any definitive answer, certainly not in the scientific literature, so any suggestions would be speculation," says Gillian Westgate, who studies hair biology at the University of Bradford in the UK.
L'Oreal conducted a study in 2012 in which trained evaluators examined the heads of 4,192 adult men and women from 23 regions of the world. Gray hair clustered at the temples in men over age 45, regardless of ethnicity. But most of men also had gray hair on the crown and back of the head, with the hair in the temples showing up with slightly higher intensity. For women in the same age group, gray hair showed up on the crown and the temples in equal measure. It's unclear from the results whether the gray hair appeared all at once or sequentially.
Another study, with participants between ages 12-91, found similar differences between men and women, with men having about 20 percent more gray hair at the temples compared to the rest of the head, which also contained grays spread equally around, as measured by trained evaluators. Women, on the other hand, had an equal distribution of grays at the temples, front and top of the head, with less towards the back. The researchers took a stab at the pattern of graying over time: In surveys, about 60 percent of men reported that grays first appeared at the temples, whereas women reported graying generally starting at the front of the head. But the reports relied on subject's memories, which the researchers noted are susceptible to recall and other cognitive biases, severely limiting the conclusions.
Indeed, when asked to estimate the presence of gray hair on their heads, men accurately estimated the amount of gray at the temples but drastically underestimated the amount around the rest of the scalp in self-reports compared to the standardized hair examinations. Women estimated the distribution of grays relatively closely. Although it's tempting to chalk this up to women having a more realistic sense of perception (ha), the discrepancy is more likely related to the heightened intensity of grays at the temples in men versus women, which could influence recall. So there might not be more grays, but what's there is the damn grayest.
"Is it just because it tends to be more visible there?" asks Paradi Mirmirani, a dermatologist in Vallejo, California and regional director for hair disorders at Kaiser Permanente. "In the course of daily living, when you look at people that does seem to be an area that kind of catches your eye."
When the real gray-spotting professionals—hair stylists—were asked about observing grays at the temples first, they deny it altogether. "I haven't seen that," says Quentin Gholar, 27, a barber at Frank's Chop Shop in the New York, who's been cutting hair for seven years. "In my experience it tends to come in all over." Hiro Nori, 34, barber of ten years working one chair over, concurs.
Although the jury's still out on whether gray hair begins at the temples, both studies show that it is more prevalent and vibrant there in men. As for why that may be, life stress is unlikely to be the root cause, as men and women experience relatively equal stress in life on average, yet show a different pattern of graying.
Gray temples likely have genetic origins, related to the way skin is formed in utero. "Local control in different regions of scalp may influence graying," Mirmirani says. "The top of scalp has one genetic signature and the sides and the back have another." As skin is being formed in the womb, a sheet from the lower neck grows upwards to form the skin around our temples and back of the head. The skin at the front and towards the crown develops from a separate plane of skin stretching upwards over our faces, with the two connecting at the vertex in the center of the scalp. The different genetic origin of different regions of the scalp has been found to be the reason behind male pattern baldness, Mirmirani says, in which hair typically depletes from the top of the head and crown and but stays in a fringe pattern around the temples. Graying appears to show something of an opposite pattern.
Another reason the temples may be more susceptible to graying may follicle cycling—the process by which hair grays. Hair pigment is produced by melanocytes, which sit around the hair bulb once formed and deliver pigment to hair in cycles. "Every hair cycle you need to rebuild your factory and you lose fidelity with every hair cycle," Mirmirani says. Hair pigment loses fidelity after four to five cycles, at which point graying sets in. Hair at the temples tends to fall out less. There is evidence that gray hair also tends to be thicker than pigmented hairs, potentially making coloring them more of a burden and less effective.
Hormones could also play a role. Hairs at the temples are rooted "more shallow in the skin and they remain sensitive to androgens," male hormones that are known to speed up hair cycling, Westgate says. "More rapid hair cycling means more opportunity for this graying effect." Sometimes the most obvious physical features of aging aren't ones that receive the most research attention. Perhaps the study of people who don't gray at the temples would reveal some clues as to whether this is due to genetic, hormonal or environmental factors, she adds.