A few years ago, Dr. David Weinstein started to lose his hair. “I really was pissed off,” he explained to me recently, in the tidy, tiny conference room of a co-working space in Manhattan. “I’m the only male in my family who managed to keep my hair! And I was in my mid-fifties, and all of a sudden it fell out. I thought, This is nuts. I don’t like this. And then I thought, I know a little bit about regenerative medicine.” Weinstein is a neuroscientist specializing in spinal-cord injuries and nerve regeneration. Working in his lab, in his spare time, he developed a drug compound he called RT1640.

Then Weinstein began experimenting on himself. “I didn’t tell anybody I was doing this, including my wife. And, after a couple of weeks, I said, ‘Look at my head.’ And she said, ‘Your hair is growing. Why?’ ”

Weinstein has big dark eyebrows and a kind face. Kind of an Elliott Gould vibe. I looked at his head. There was a spotty, thatchy outcropping of gray-black hair. Not exactly an overflowing abundance, but hair, to be sure. “I had nothing on top,” Weinstein said. “You can see—I grew my hair back! And it grew back more or less the color I had when I was young.”

Weinstein founded a company to develop RT1640 for the consumer market. That company, RiverTown Therapeutics, is to date tiny and unknown. But Weinstein is confident that he’s discovered the cure for hair loss. Which would mean that he has found the solution to an ancient problem with an eternal stigma.

In II Kings 2:23-24, the prophet Elisha is mocked by a gang of surly kids. The kids “said unto him, ‘Go up, you bald head! Go up, you bald head!’ ” Elisha “cursed them in the name of the Lord.” Promptly “two she-bears came out of the wood and tore forty-two of them.” Sometime later—in 2013—German researchers published a study indicating that men experienced hair loss as an “enormous emotional burden” that could lead to an “impaired quality of life” and “psychological disorders.” Inversely, one study has shown that people perceive men with bountiful hair as likely having big penises.

People are also much, much more likely to vote for political candidates with hair. Only five elected American Presidents—John Adams, John Quincy Adams, Martin Van Buren, James Garfield, and Dwight Eisenhower—were bald or balding. Considering that eighty-five per cent of men older than fifty suffer hair loss, that’s an astonishing record.

It is no surprise that Donald Trump is obsessed with hair loss. “Never let yourself go bald,” he once told a Trump Organization executive. “The worst thing a man can do is go bald.” During their brief dalliance, Stormy Daniels confronted him about his hair. “I was like, ‘Dude, what’s up with that?’ ” she said, to In Touch, in 2011. Trump laughed. Then he told her that he worried that “if he cut his hair or changed it, that he would lose his power and his wealth.” Recently, Trump’s physician admitted that the President takes the anti-baldness medicine Propecia.

Hair growth is a giant industry, with estimated annual sales of $3.6 billion. And every one of those dollars goes to products that do not provide actual hair regeneration. Rogaine and Propecia, the market leaders, can slow hair loss, but they don’t grow new hair. They also come with the small risk of serious side effects. In 2011, Men’s Health reported on a Propecia user who “lost all pleasurable sensations in his penis.”

Quietly, however, progress churns. Joseph is the pseudonymous proprietor of the Web site Follicle Thought, a popular destination for hair-loss obsessives. Follicle Thought is dedicated to “what’s next,” Joseph told me. “What could be coming? Obviously we have other things to cure. But, like, what is the world doing about hair? Hundreds of millions of people really want it. It’s a really deep, emotional, psychological issue for people.” He paused. “I’ve put so much thought into that question.”

Joseph and his readership, he said, are convinced that we are at a “peak moment” for the industry. He ticked off “platelet-rich plasma” and “injectable cell therapies” and other high-level technologies that are being developed by companies from New York to San Diego, Tokyo, and Stockholm. He won’t make bets on who’s going to win the arms race. But, he says, “if you were the first, that’d be fun for the trillion dollars that you’d make. Over the next few years? It’s prime time.”

In the nineteen-forties, a Brooklyn anatomist named James Hamilton studied prisoners in Oklahoma who, having been convicted of sexual assault, were castrated. Hamilton identified testosterone as the root of hair loss, and showed that men castrated before or during puberty did not go bald. He then injected groups of castrated adult men with testosterone and—duly, cruelly—watched their hair fall out.

In the following decades, researchers learned that testosterone does not work alone. An enzyme converts testosterone into a substance called dihydrotestosterone, or DHT, which causes hair follicles to shrink. DHT attacks the dermal papilla, the “brain” of the hair follicle, and is the main cause of male-pattern baldness, which affects more than fifty million men in the United States and also—largely unremarked upon, but true—more than thirty million women.

Rogaine and Propecia, the only commercial hair-loss products that have ever been proven to work, were both discovered accidentally. Rogaine, a topical product known as minoxidil in its generic form, was originally developed as a blood-pressure drug. Scientists do not fully understand its efficacy, but the working theory is that minoxidil protects the dermal papilla from DHT. Propecia, or finasteride, was originally developed as a treatment for enlarged prostates. It inhibits the creation of DHT. Both products have drawbacks. In order to be effective, minoxidil must be applied daily. Because of the hormonal imbalance that finasteride causes, women can take it only if they are postmenopausal. If you stop taking either drug, you will quickly lose the hair you would have lost in the duration of your usage. (Recently, on the actor Dax Shepard’s podcast, Ashton Kutcher confided that he’d stopped taking finasteride. With awe, Shepard said, “I just think that’s so risky of you.”)

Gersh Kuntzman is a newspaper and magazine lifer and a semi-professional hair historian. In 2001, he published “Hair!: Mankind’s Historic Quest to End Baldness,” a slim, delightfully strange book that is one of the only comprehensive non-academic studies of the field. “There is nothing that can regrow hair once a follicle is destroyed,” he wrote.

I met Kuntzman on a hail-heavy day, in the bottom lip of Manhattan, and we walked to a pizza-by-the-slice place. “I’ll have the Gersh!” he shouted to the man behind the counter. The man was befuddled. The man’s co-worker stepped in and gave Kuntzman a nod of recognition. A Gersh—a hot chicken-parm sandwich with spinach—soon appeared.

“People have been trying to sell a baldness cure since the beginning of civilization,” Kuntzman explained. “And the methods by which they try to sell that cure have not changed dramatically. These new companies, they’re trotting out the same promises that people trotted out in Roman times, when they said, ‘Use this hippopotamus fat to grow hair on your head!’ ”