TOKYO -- For hundreds of years the Japanese have enjoyed nightly baths. Now, younger Japanese have added a new ritual, the morning shampoo, and their elders are wondering if all this cleanliness doesn't add up to overindulgence.

The daily morning shampoo, known as "asa shan," has become a symbol of youthful excess in Japan -- excess chemical use, excess energy use, excessive narcissism.

It highlights a gap between the generation that toiled to rebuild the country from the ashes of World War II and its offspring, which has known nothing but affluence.

At best, analysts say, the trend toward fastidiousness is a harmless fad, fueled by manufacturers trying to expand stale markets for personal cleaning products.

At worst, "Asa Shan Will Destroy the Country," screamed the title of a recent article by Hiroshi Inamura, a Tsukuba University professor of public health.

Others are just plain puzzled by the physical cleanliness obsession among the young.

As cultural anthropologist Masao Kunihiro put it, "Excessive preoccupation with one's bodily cleanliness ... appears to be bordering on a kind of disease."

In the past, daily shampoos were rare in Japan because of the lack of electric hair dryers, the difficulty of heating baths with wood or coal and the custom of all members of a family sharing the same bath water, said Mizue Sasaki, an English professor at Yamaguchi University.

The spread of showers and gas heaters in the 1960s and 1970s made washing easier, increasing the frequency of nighttime shampooing.

Then, about two years ago, Shiseido, Japan's leading cosmetics maker, came out with a combination shampoo and rinse marketed specifically for a second daily hair washing in the morning.

The result was a new niche in what had been a stagnant shampoo market, said Mitsuo Ohmi, a pharmaceuticals analyst for Barclays de Zoete Wedd Securities.

Other companies responded with a flood of new products, including extra-large sinks and super-absorbent towels. Other personal hygiene products, from deodorants to mouthwashes, wet wipes and antiseptic sprays for toilet seats, took off at about the same time.

But some see more than markets at stake.

Worrying more about cleanliness than more practical or spiritual concerns could weaken the moral fiber of the nation, wrote Inamura, a medical doctor, in the latest issue of Shokun magazine.

Besides, people too worried about cleanliness would become intolerant and "would tend to avoid unclean people," Inamura wrote. He deplored Japanese children who frequently call each other "smelly" or "germ."

Others believe the fad for fastidiousness borders on the physically harmful.

Kaoko Yamamoto, a 42-year-old mother, wrote in a letter to the Yomiuri Shimbun, Japan's largest daily newspaper, that each day her child bathes up to three times, changes clothes up to three times and pulls on a fresh pair of socks up to four times.

"In our time, we were told that too much hair washing causes baldness. A wash once a week was enough," she wrote.

Medical experts quoted in recent magazine articles and anti-cosmetics books, such as one published last year titled "Why Do You Want to Make Up?," warn that shampoo chemicals can be harmful to hair and scalp skin.

Cosmetics companies dismiss such claims.

Asa shan -- "asa" means morning and "shan" is a contraction of the Japanese phonetic spelling of shampoo -- also has come to symbolize the energy-intensive lifestyles of young people.

Tokyoites use the equivalent of roughly 190 million gallons of oil annually for asa shan, according to a government report on energy conservation published this year.

Tsutomu Toichi, chief economist of the independent Institute of Energy Economics, said "asa shan" was "an easily understood example" of the problem of high-energy lifestyles in Japan.

Almost everyone agrees the morning shampoo controversy is a symbol or symptom of a generation gap.

"Young people today have few goals in life. Cleanliness has become a status symbol," said Kenshiro Ohara, a psychiatry professor at Hamamatsu University School of Medicine.

Their parents and grandparents, by contrast, "were poor, but their hearts were completely clean."