Need to beat the heat? With record-breaking temperatures this summer, it is no wonder that "cool shampoo" has taken off nationwide.

The cool shampoo service originated in Yamagata, which is one of the nation's hottest cities.

Hairdresser Koichi Onuma, 43, came up with the idea during a searing Yamagata summer 15 years ago.

He had returned from Tokyo to open his salon, and one day saw a sweaty customer enter his shop. Onuma thought, "What can I offer my customers so they really feel summer but makes them cool as well?"

Onuma came up with the idea of cooling a menthol shampoo in the fridge to 0 C, which he tried out on a regular customer. "It feels like I was reborn!" the customer said, describing the sensation as exhilarating, like the shampoo was passing through his scalp.

Seeing this reaction, Onuma began regularly offering the service during summer to his clients.

He named the service "hiyashi shampoo" (cool shampoo) after "hiyashi ramen" (cold ramen noodles), the city's popular summer local dish.

Other hairdressers soon followed suit, and by 2008, about 300 hair salons were offering the service in Yamagata Prefecture alone.

Always on the lookout for the latest trends, a TV program picked up on the service during the same year, leading to a cool shampoo boom across the nation.

Recently, more extreme shampoo services--a shaved ice version being one such example--have appeared.

However, when Onuma visits other cities to demonstrate the cool shampoo service, he advises caution as excessive stimulation may affect blood pressure or have other adverse effects.