According to the Oxford English Dictionary, scab was first recorded in English around 1250, and referred to diseases of the skin. Two hundred years later, it appeared with the common definition we know today, a hard crust that forms over a wound.

The word had taken on a secondary meaning in England by the 1500s. As a slang insult for a “mean, low, ‘scurvy’ fellow; a rascal, scoundrel,” it drew a connection between that person and scabs—and the diseases and sores that lead to them (syphilis, for example)—and, by extension, bad habits and unclean lifestyles.

By the late 1700s, laborers adopted the insult to refer to workers who wouldn’t join a strike, a union, or take part in organized labor and undermined their fellow workers. One of the earliest known recordings is from 1777: “the Conflict would not been [sic] so sharp had not there been so many dirty Scabs; no Doubt but timely Notice will be taken of them.” Early in the next century, scab became even more specialized and started being applied specifically to workers who crossed picket lines to take the place of striking workers, as in this testimony from the trial of striking Philadelphia bootmakers: “I concluded at that time I would turn a scab, unknown to them, and I would continue my work and not let them know of it.”

In her book Household Words, Stephanie Smith draws a clear line from the one definition to the other. As she writes, “From blemish … to strikebreaker, the history of the word scab … shows a displacement of meaning from the visceral or physical to the moral register … Just as a scab is a physical lesion, the strikebreaking scab disfigures the social body of labor—both the solidarity of workers and the dignity of work.”

Its power seems to have diminished a bit since the days when a piece of union literature, generally attributed to author Jack London, said, “After God finished the rattlesnake, the toad, the vampire, He had some awful substance left with which He made a scab … When a scab comes down the street, men turn their backs and angels weep in heaven, and the Devil shuts the gates of Hell to keep him out. No man has a right to scab so long as there is a pool of water to drown his carcass in, or a rope long enough to hang his body with.”

They don’t make insults quite like that anymore.

A version of this story originally ran in 2012; it has been updated for 2023.

This article was originally published on www.mentalfloss.com as The Reason Why People Who Cross Picket Lines Are Called ‘Scabs’.