A Chinese schoolteacher has become an overnight internet sensation after a video urging her students to wear “tasteless” long johns to keep warm went viral.

The video was shared by parents everywhere, who hailed the teacher, surnamed Cheng – from the Yuhua Experimental School in Kaifeng, in the central Chinese province of Henan – for being warmhearted.

Commonly worn in China’s colder climates, long johns – known as qiuku in the country’s northern provinces and mianmaoku in the south – are elasticated, stretchy tights generally made of cotton and fine wool that cling to the skin, trapping body heat to insulate against cold air. They are generally worn with a long-sleeved clingy top of the same material.

Sub-zero temperatures in central China last week prompted the caring teacher to make the video after an inspection of her students revealed that two students were without the protective garments underneath their trousers.

Although only a girl and a boy were chastised for failing to wear their long johns, Cheng took the matter seriously enough to go the extra mile and make an instructional video for them.

In the endearing video, Cheng shows students how to dress properly by tucking their long johns into their trousers for the winter to avoid colds and other illnesses.

“Inserting the bottom of your long johns inside your socks is the basic respect for winter,” Cheng says.

She went on to explain that most teenagers don’t like to wear long johns even when the temperature falls below zero degrees Celsius (32 Fahrenheit).

“Kids are still growing up. If they catch a cold by not wearing enough clothes, it’s not good for their health,” said Cheng.

While appreciative viewers praised the instructional video, it was Cheng’s genuine concern for her students that pulled at the heartstrings of grateful parents everywhere and made the teacher an overnight internet sensation.

“Kids nowadays are very obstinate. We parents tell them repeatedly to wear long johns, and they just won’t listen,” wrote a user on social media app WeChat. “This teacher’s sudden inspection is useful. Those students’ parents will feel very relieved.”

“This teacher is so responsible for her students. I wish my son could have a teacher as warmhearted as she,” wrote another person.

However, style-conscious Chinese youth are shedding long johns in the belief they are “tasteless” and “old-fashioned” because they are not worn in the West.

In the United States and Europe, thermal long johns are generally reserved for use on the snow fields under ski gear to ward off the effects of extremely low temperatures.

Instead, the younger generations prefer to follow current fashion trends by wearing ankle-skimming, three-quarter-length skirts and pants.

One reason long johns are popular with older people in China’s colder climes is that traditional Chinese medicine (TCM) claims that keeping warm has health benefits. In particular, TCM recommends keeping the lower limbs warm to combat illnesses including arthritis.

Earlier this year, a high school student from Changsha in Hunan province, south central China, was told by a doctor to wear long johns as a treatment for his chilblains – a painful inflammation of the skin after long exposure to cold air that causes itching, swelling and redness.

Along with ointments to alleviate the symptoms, doctors prescribed wearing long johns under his “thin jeans” during the colder weather, according to local news network rednet.cn.

“My mother has prepared long johns for me, but I, an iron man, won’t wear them,” he was quoted as saying. “My classmates will laugh at me if I wear them. Although it is a bit cold, I can bear it.”