Zeph Sanders was 20 when his hair began to fall out. As it thinned from the density of AstroTurf to spare wisps, he hid his head under a beanie before logging on to play video games on the livestreaming platform Twitch.

“I started getting people in the comments like, ‘Bro, where’s your hair?’” Mr. Sanders, now 27, said on a recent video call from his home in Orange County, Calif. “I felt a little bit more insecure as the days went on.”

Last year Mr. Sanders allowed a glimpse of his bare scalp in a video he posted to TikTok. It took off, eventually passing four million views. Hundreds of commenters suggested supposedly miraculous regrowth methods, which Mr. Sanders began trying out in his windowless bathroom, with his iPhone camera rolling.

A year later, he has sprouted a fine fuzz across his crown and 600,000 new followers on TikTok. His haters haven’t gone anywhere: “bro give up,” one wrote on a recent video, adding the crying-laughing emoji.