The veneration of relics is one thing many religions can agree on. From Buddha’s tooth in Sri Lanka to St. Anthony’s tongue in Italy, the faithful flock to witness—and worship—the bodily remains of holy figures, through which the grace of some higher power is believed to flow. Hair has always been one of the more abundant relics: It is easily harvested and a person generally has a lot of it, a fact which prevents awkward questions arising about authenticity. (In the Middle Ages, it emerged that a dozen different churches claimed to be in possession of Jesus Christ’s foreskin.)

Hair is also one of the few relics that has retained its currency in secular circles. In the Victorian era, preserving the hair of loved ones became a popular pursuit: Families would weave their tre...