KATHMANDU, Nepal — When Amba Bohara’s period came this week, she followed a familiar routine in western Nepal. Considered impure in her village because she was menstruating, Ms. Bohara barricaded herself in a tiny hut, built a fire and braced for an icy winter night with her two young children.

By Wednesday morning, all three were dead.

“It seems they died from suffocation,” said Uddhab Singh Bhat, the deputy superintendent of police in the area. “The hut was so small. It was very difficult to breathe.”

Ms. Bohara and her children were the latest victims of a centuries-old tradition of banishing menstruating women and girls from their family homes. Though Nepal criminalized the practice last year, many villages in the country continue to follow the taboo, known as chhaupadi in Nepali.

During their periods, women living in places where chhaupadi is followed are unable to visit temples, use other villagers’ kitchen utensils or wash in communal water sources. Some religious Hindus consider it bad luck to touch menstruating women and girls.