Photos of Barack Obama acknowledging his second-term election win show a man a world away from the fresh-faced young victor of four years ago.
Alongside the sense of relief etched on Obama's now heavily-lined features, it was hard not to be struck by another physical manifestation of power - he has gone badly grey.
Halfway through his eight-year term, Obama's hair is a bellwether of the unrelenting pressure heaped upon the man known as 'Leader of the Free World'. It tells the story of his Presidency so far as articulately as the US deficit or employment figures.
The President's once dark and closely cropped locks are now streaked with grey and palpably thinning on the crown and around his temples.
Indeed, Obama, whose youthful bearing and demeanour was a big part of his original sell to voters, admitted recently: 'I'm full of grey hair, but I'm not weary.'
While his crow's feet and greying hair are only the most visible signs of the pressure of his job, it would be a mistake to underestimate their import.
These very visible physical manifestations of stress are not simply a gift to the world's picture editors, and hair transplant surgeons like myself. They are an outward indicator of the internal difficulties of leadership in the modern world.
And Obama is not the first powerful man - and it is mainly men affected in this way - whose hair has suffered and signalled the strains of his job.
Nor will he be the last to display such physical symptoms of leadership.
Tony Blair went into office as British Prime Minister with lush brown hair and a sense of tennis-playing energy. Like Obama, his relative youthfulness was part of the anti-John Major sell to British electors tired of the grey men of the Conservative party.
After a decade in power, Mr Blair's hair had receded dramatically around the temples and on the crown, and was visibly thinning and streaked with grey.
Frankly, he looked exhausted.
Campaigning last week for elected police commissioners on behalf of his former Labour colleague John Prescott, Mr Blair looked much better.
He's got some of his facial colour back, and his hair looks healthier, but his decade at the coalface as PM aged him dramatically.
Unsurprisingly, it was the same for his successor, Gordon Brown.
Despite being nicknamed the 'Iron Chancellor', he became PM in 2007 with just a few steely streaks in his otherwise raven-dark hair.
By the time he left Downing Street, having gone toe-to-toe with global economic meltdown and a bitter and ultimately fruitless election battle, his hair was streaked in battleship grey. Truly an iron man, at last.
David Cameron, who was only 43 when he became PM, was showing greying hairs within a few months.
Human hair becomes grey - then progressively whiter - because ageing naturally lowers the amount of pigmentation in follicles.
This pigmentation, known as melanin, ceases to be produced by the body in sufficient amounts as we grow older. As this happens, new hairs appear grey, then white.
But it's not just our age that affects hair colour.
Family genes and stress - divorce, unemployment, a high-pressure job - can all play a role.
President Obama's job and age - 51 - make him high risk for greying and male pattern baldness. The latter is the main cause of hair loss, affecting an estimated quarter of men by the age of 30 and two thirds by the age of 60.
The bad news for Obama is that when he does retire in another four years - presumably to something less stressful - his hair won't return to its original colour.
Sadly, it's very common for those in high-powered jobs to suffer premature greying.
Stress, and changes in levels of the male hormone testosterone that a high-pressure job with long hours, high anxiety and lack of sleep can engender, play havoc with hair colour and density. In the very worst cases, they can trigger total hair loss, alopecia.
I'm not suggesting the 44th President of the United States needs a hair transplant. His hair loss is mild, but he should look after it. I'd recommend using the drug Propecia to help prevent any further loss of density and a special shampoo to nourish his roots.
After all, in today's society image is vitally important. The fact Obama himself mentioned his greying hair tells us that much.
For the President to project America as ready for the next challenge, with a new sense of energy and urgency, as he has done, it couldn't hurt for him to look and sound a bit more like the youthful Senator from Illinois of four years ago.
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