Open this photo in gallery Justin Trudeau attends a press conference in Ottawa on Jan. 8, 2020. BLAIR GABLE/Reuters

Mark Kingwell is a professor of philosophy at the University of Toronto.

Facial hair doesn’t usually merit an appearance in the news, but Prime Minister Justin Trudeau’s decision to sport a beard is the clear exception. When our young leader chose to adorn his handsome face with what satirists from Frank Richardson to Kingsley Amis have derided as “face fungus,” the country rubbed its collective chin and noticed.

Speculation has run riot – well, maybe semi-riot. Was Mr. Trudeau trying to look older and more distinguished? Or was he, per contra, trying to look younger and more hip? Beards are unpredictable sprouts, especially when you first develop one and then appear in public. I am not alone in having made the ill-advised choice, during philosophy graduate school, to sport a scraggly “sage” version. One of my friends laughingly told me she had been pretty sure that my twentysomething fresh-faced Celtic-Austrian cheeks would not support even a pathetic barbe.

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Beards have a long history in civilization, considered a mark of manliness and strength. Beard hair is a function of testosterone, after all. There are famous bearded characters real and imagined: Redbeard (pirate Hayreddin Barbarossa), Blackbeard (pirate Edward Teach) and Bluebeard (folktale wife murderer), not to mention Fidel Castro and Che Guevara, Ayatollah Khomeini, George Michael with his designer stubble, and Santa Claus. Fun fact: Edmund Gwenn’s Santa beard in the 1947 version of Miracle on 34th Street was famously genuine and tuggable.

Athletes sometimes wear beards to look more fearsome. San Jose Sharks centre Joe Thornton has a luxuriant, borderline out-of-control growth of wiry grey that makes him look like an angry caveman on skates. Former San Francisco Giants reliever Brian Wilson used to appear with a jet-black face number that, alas, turned out to be dyed. Mr. Wilson was cheered with “Fear the Beard” chants during his appearances – an honour that now belongs to the NBA Houston Rockets step-back jump shot artist James Harden, known simply as The Beard.

Baseball scholars will recall that the legendary Michigan-based House of David touring squad, missionaries and cultists in pinstripes, had long flowing hair and beards. Legendary cricketer W. G. Grace was celebrated as much for his fulsome whiskers as for his deft cuts to square leg.

Mr. Trudeau’s version has been described as salt-and-pepper, a polite term for grey. He looks older and more serious wearing it, arguably less feckless. He had just returned from a sojourn in Costa Rica when spotted in this new fungal fashion, suggesting a vacation of casual neglect.

Marshall McLuhan is supposed to have commented to Mr. Trudeau’s father, who grew a beard while in Opposition, that he was “cooling” his image. Mr. McLuhan’s notion of “cool” has to do with the degree of interaction required of a viewer, not hipness. Thus sunglasses are cool because they hide the eyes, beards because they hide the face. By contrast, a clean shave is an open book.

Which perversely recalls a fashion consultant who years ago advised a hapless then-prime minister Joe Clark to grow a beard in order to “hide his unfortunate chins.” (Yes, it was plural.)

All of this is pretty silly, but we know politics are all about image. Mr. Trudeau, the former drama teacher, never does anything without considering impact – though not always wisely – including yoga poses, goofy Indian costuming and unforgivable brownface. Two worries occur to me, though, speaking as someone who shaves only every couple of weeks and therefore has a beard mainly through inattention.

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The first is that grey beards are a dicey proposition. There is a website, favoured among my graduate students, called Prof or Hobo? You choose which category a given male face belongs to, and then your results are scored. It is weirdly addictive; with no disrespect to either group, it can be hard to tell them apart, especially if they’re past 50. Mr. Trudeau is, for the record, 48.

Second, an Australian friend of mine argued a while back that we had reached what he called Peak Beard. This was when the term “lumbersexual” was still in use and every coffee shop or bike courier depot thronged with young blades flashing waxed moustache tips, expensive jojoba-oil treatments and elaborate trims. A later television ad mocked two well-muscled dandies in sharp beards and flannel shirts carving artisan cocktail shavings from an iceberg. That ship has literally sailed, guys.

Mr. Trudeau must govern himself accordingly. It happens that there is a real thing called beard fungus, a kind of ringworm. Yuck. Exfoliate, sir, exfoliate.