Kailali, Nepal - Four feet high, four feet wide.

This is the size of the shed where Durga Buda, 31, spends four nights every month. Known as a "goth", it is made of bamboo, straw and wood; walls are caked with mud and cow dung.

"Now I am used to it, but the fear of wild animals, snakes and drunkards is always there," she says.

At night she uses a thin wool blanket, frayed at the edges. Some holes in the mosquito net are stitched, some patched with safety pins. Her family of eight, including in-laws, sleep in a mud-brick house - but she is exiled to the backyard, next to two cows and six goats.

Buda is following the centuries-old chaupadi ritual, prevalent in far and mid-western regions of Nepal. During menstruation and childbirth, women are isolated to a cowshed, hut, barn or cave because they are believed to be impure - their touch is said to contaminate - resulting in doom for the family, neighbours and domestic animals.

It is said if we touch men or anything in the house, cook or use public water tanks and wells, our God, Debti, will punish us. Our hands and legs will be twisted, our eyes plucked out. - Durga Buda, 31

During Buda's first period, she was segregated for 11 days, "I was scared, cold and confused. But the fear of sin was bigger," she says.

The Hindu tradition is common to all castes in the region. Women who violate the practice are blamed for crop failures, illnesses and sudden deaths of animals. "Who wants to be ostracised?" she asks.

Monthly exile

There are reports of chaupadi leading to deaths, attacks by wild animals, snakebites, diseases, rapes, poor mental health, and infants dying of pneumonia. A 16-year-old girl suffocated to death in her goth. In recent years, some women have turned their back on the ritual: a few burnt their sheds, and some villages are known as "chaupadi-free zones".

But although the country's supreme court banned practising chaupadi in 2005, the custom dies hard. It remains firmly rooted in many villages, especially in remote hill areas. A 2011 report estimated that 95 percent of women in Achham district follow it.

By sunset Buda has finished eight hours of work, cutting grass and collecting wood. Lunch and dinner consists of flatbread and salt. Meat or dairy products are prohibited.

"It is said if we touch men or anything in the house, cook or use public water tanks and wells, our God, Debti, will punish us. Our hands and legs will be twisted, our eyes plucked out," Buda explains. Fruits will rot, cows will stop giving milk, wells will dry up, houses will burn and tigers will attack at night.

Even so, when Buda gave birth the first time she had doubts. "It should have been a joyous event, but I was alone for 11 days - nursing, feeding, cooking and cleaning. I almost refused to stay in the shed." But she was afraid of bad luck befalling her son. More than 80 percent of women give birth at home in Nepal.

She remembers thinking, ''I had to be strong like my mother and the women before her."

'Gender violence'

Aruna Uprety, a doctor and women's health rights activist, calls chaupadi a form of gender violence and the "most degrading" cultural practice in Nepal. She has written a book called Chaupadi: a Harmful Practice for Women.

Discriminating against women because of their bodies' natural processes is a crime, she says. "We cannot identify the perpetrator as man or woman. The religious and cultural leaders are to blame."

[The] government banned it, but there is not a single case of punishment, fine or reprimanding. - Aruna Uprety, doctor and women's health rights activist

Older women justify the practice, saying that in earlier times, sanitary pads or undergarments were not used. Menstrual blood would flow out, leading to a foul smell, so women were sent to outhouses. The same conditions existed in eastern Nepal but there is no chaupadi there, Uprety argues.

During the 10-year Maoist insurgency, many goths were razed. "Instead of creating awareness leading to create social change, they [the Maoists] used force. When the peace process started, the goths were rebuilt," Uprety says. Many Maoists and even some female anti-chaupadi activists follow the tradition. Schools give paid leave to female teachers during menstruation, and menstruating students are not allowed to attend classes.

The dread of divine wrath cuts across class, caste, education and ideological divisions. "Imagine the shame and mental agony when school officials, your family, your whole community keeps account of your menstruation cycle," Uprety says. Some women pray for early menopause; others gulp down Depo-Provera, a contraceptive that temporarily halts menstruation.

In recent times, feminist groups and developmental agencies have published booklets and posters and launched radio programmes and awareness drives in communities and schools. Nowadays, in some villages, women sleep in a separate room in the main house instead of in outhouses. But they are still untouchable.

"[The] government banned it, but there is not a single case of punishment, fine or reprimanding," Uprety adds.

Generational debate

Nepal's far and mid-western regions make up half of the country's area and 23 percent of the population. Just under half its people live under the poverty line. Apart from underdevelopment and gender inequality, major challenges in the area include caste discrimination, unemployment, seasonal migration to India, widespread child and bonded labour, malnutrition, high infant and maternal mortality rates, low literacy and poor connectivity because of difficult terrain.

Nepali women segregated during menstruation

Lalaji, a village elder in Achham, believes the tradition should be respected. "The new generation wants to change things. But as long as we live we will teach them what is right and ask them to follow our Hindu culture," he says, sitting on a cot chewing betel nuts. "Many people have fallen sick because of eating food cooked by menstruating women," he adds.

Some younger men oppose the practice, like 27-year-old Ramesh Bhatta of Dhangadhi. "I know it is very tough for women to live alone, so far from the house. I feel bad. It is unfair that we sleep in comfort, while they are exposed to danger."

Tulsi Devi is a grassroots volunteer with Feminist Dalit Organization in Kailali district. "Some of us refused to follow the custom. We were able to convince a few families to change. But older women are strong believers of this system and want their daughters and daughters-in-laws to follow these customs," she says.

She shares her story with other women to quell their fears and doubts. "I say 'look: My cows and chickens are fine, we still have a harvest, my body is normal'."

She is lucky her family supported her. "Women cannot decide what is safe, what is good for them. Everyone has a say."

Devi points to a mound where her goth once stood. The only remaining sign of its existence is a bamboo stump, sticking out among overgrown weeds.