Sarifah Nurhayati is five months’ pregnant with her second child. Her post-partum plan, she says, includes getting her vagina “back in good shape to keep my husband happy”.

The 27-year-old, who lives in Depok, in greater Jakarta, plans to use a tongkat Madura, or Madura stick – a cigar-shaped product promoted as a sexual-health aid that erodes gradually in the vagina – to achieve that goal.

The stick leaves the vagina drier, tighter and stronger, she says. Some experts, on the other hand, warn that it could also cause infection.

Sarifah says she slides the stick into her vagina and leaves it for two to three minutes before taking it out. When finished, “just wash the stick, air dry it, put it back in the box, and you can use it again”, she adds. Sarifah can use one 20 times before replacing it.

“When used regularly, it will make you feel like a virgin again,” she explains, adding that she has been using the tool for four years.

Sarifah’s husband, Reno Waldi, sells Madura sticks in his Depok shop. “An average of seven to eight sticks are sold each day here,” he says. “The prices define the quality of the sticks. The cheaper they are, the easier they break. You don’t want that to happen while using it.”

Reno sells various types of traditional herbal medicines, popularly known as jamu, condoms, and Madura sticks in his modest three-metre by four-metre (10ft by 13ft) store on a busy road.

“This is a family-owned business that was started 18 years ago, and we have been selling tongkat Madura ever since,” the 29-year-old says. “As far as I know, we have never received a single complaint about the sticks.”

Named after Madura, an Indonesian island off the northwest coast of Indonesia’s most populous island, Java, where it first came to prominence, the tongkat Madura has been around for decades. Judging by the large number of online advertisements, sales of the sticks have boomed across Indonesia in recent years.

There are three large producers and a number of smaller ones. The tool is not government-approved, however, no official sales records exist, and there have even been complaints of fake products being sold on the internet.

Ads list ingredients including herbal extracts and other “secret” ones, and claim the sticks help women achieve stronger pelvic floor muscles and a tighter vagina, as well as keeping it dry and eliminating bacteria and infections.

Madura sticks cost from US$3 to US$30. One brand, Jokotole, sells for US$5; inside the box is a hard, slightly rough stick 10 centimetres (4 inches) long, double-wrapped in a thin protective foam sheet and plastic bag. There is an information sheet in the package but it does not list the ingredients.

“I know it doesn’t say what it is made of but I believe everything is natural,” Sarifah says. “I’m not scared [of using it] because we have personally felt the benefits.”

Boyke Dian Nugraha, an Indonesian doctor specialising in obstetrics and gynaecology, doubts the Madura stick has any genuine benefits.

“There are vaginal tablets produced by pharmaceutical companies, but they have been clinically or medically tested,” he says. “And this is not the case with these sticks.”

Boyke fears the use of Madura sticks may lead to serious health problems, including cervical and vaginal cancers.

“If produced unhygienically, they may carry HPV viruses, known as the cause of those types of cancers, and also other viruses that trigger the growth of genital warts and herpes,” he explains. “And you’ll never know if the manufacturers also use carcinogenic materials and heavy metals in the mix.”

Contrary to the claims of tongkat Madura producers, the sticks are more likely to cause women pain if the chemicals dry up the vagina’s natural lubricants, he says. The friction of sex could then be painful.

“I don’t think they will feel comfortable because it irritates the vagina,” he says. “And irritations may lead to infections.”

A former seller of Madura sticks, Uswatun, says the discomfort is bearable. “It’s painful for me during sex, but my husband really likes it, so I’m OK with that,” she says. “It makes him happy.”

Mayagustina Andarini from the BPOM, Indonesia’s drugs and food control agency, confirms that Madura sticks have not been approved and are therefore illegal.

“There is no valid reference as to what plants are used in the Madura sticks’ concoction. Besides, the application of traditional medicine using intravaginal administration is not allowed according to regulations issued by the head of BPOM,” says Mayagustina, who supervises the agency’s department of traditional medicines and health supplements.

A number of tongkat Madura makers declined to comment on their products’ licensing, but vendor Reno says that sales have nevertheless been stable for many years.

Irwan Martua Hidayana, an associate professor in the anthropology department at University of Indonesia, says that although the history of Madura sticks is unclear, their popularity may have a lot to do with the country’s patriarchal ways.

“Indonesia is culturally diverse,” he says. “However, when it comes to sexuality, there is a tendency for males to have a more dominant role than females.”

It is often men who initiate sex because women have been taught from a young age to control their desires, he says, and they are expected to be serve their husbands well.

“In general, it is considered normal for a man to have premarital sexual experiences, while women have to stay virginal until they get married,” he adds. “This is what created the perception that wives have to be able to make their husbands happy. And that is the gender construction that exists here [in Indonesia].”

Postgraduate student Agung Sandi Perdami was born into a Madurese family and had a traditional upbringing. He recalls his parents taught him and his sister differently as children.

“Being part of a patriarchal society, my parents emphasised the importance for me, as a male, to be a leader,” the 23-year-old says. “So, they introduced me to Madura’s traditional martial arts when I was only five – apart from learning to recite the Koran in the mosque. Meanwhile, my sister was taught to be good in the kitchen, but she was also taught to respect the male members of the family.”

The Madurese people, Agung says, “firmly believe that a man’s happiness is the key to the whole family’s happiness”. In their culture, he says, when a married man has an affair, the wife is often blamed for “not being able to satisfy the husband”.

Women are expected to be really good at sex, he adds. “Therefore it is common for those about to get married to be given a Madura stick by their mothers.”

Boyke recommends any women who have used the sticks to get a Pap smear, to detect any potential precancerous and cancerous growths in the cervix. “But most importantly, stop using the stick immediately,” he says.

For loyal user Sarifah, however, a Madura stick is irreplaceable. She insists that unless she is pregnant, she will never stop using one.