In the two decades that Angela Smith has been a hairstylist in Chicago, she has heard countless intimate stories from the women who have sat in her chair. Most times the banter is carefree. But sometimes, there are whispers of mistreatment by spouses or partners, of being choked, chased or emotionally abused.

“They say that the hairdresser gets all the secrets,” Ms. Smith said. “They let go here. Everybody doesn’t talk, but once you build a relationship with someone, that’s when it happens. It’s just like when you have a best girlfriend.”

A new state rule taking effect on Jan. 1 recognizes that the unique relationship between hairdressers and their customers may help curb domestic abuse and sexual assault. The amendment to a law that governs the cosmetology industry will require salon workers to take one hour of training every two years to recognize the signs of abuse and assault and will provide them with a list of resources to which they can refer clients for help.

Without the training, cosmetologists in Illinois will not be able to renew their licenses. The professionals covered by the rule — believed to be the first in the nation — include hairstylists, nail technicians and aestheticians.