KATHMANDU, Nepal — The last time anyone saw Gauri Kumari Bayak alive, she was gathering grass and firewood. Considered impure because she was menstruating, she was about to sleep outside in a cold hut.

She never woke up.

According to the police, Ms. Bayak is the latest victim of a very old tradition in rural Nepal, in which religious Hindus believe that menstruating women are unclean and should be banished from the family home. She was found dead on Monday, apparently having asphyxiated after building a small fire inside the hut to keep warm.

In Nepal, one of Asia’s poorest countries, dozens of women and girls have died in recent years from following this tradition, despite activists’ campaigns and government efforts to end the practice.

Menstruating women often trudge outside at night to bed down with cows or goats in tiny, rough, grass-roofed huts and sheds. Many have been raped by intruders or died from exposure to the elements.