Cosmetic surgeons in Seoul say they are seeing a sudden rise in demand for the so-called smile surgery this year among men and women in their 20s and 30s, most of whom are concerned about facing criticism at work because of their expressionless miens.

'Even when you are looking like your normal self, people keep asking you: 'Why are you frowning?'' said Kwon Taek-keun, a plastic surgeon in practice for 20 years and known in professional circles as the first in the country to popularize the procedure. 'That's a lot of stress.'

The pictures and video clips that Dr. Kwon's clinic, Aone Plastic & Aesthetic Surgery, posted online have caused a controversy in recent days, attracting derision from some media reports and the blogosphere, and comparisons to the Joker character from the Batman series.

But the cosmetic surgeons who carry out the procedure argue people, young and old, come psychologically scarred by hurtful remarks about their naturally downturned lips, especially if they have customer-facing roles. Services-industry workers such as flight attendants and consultants frequent the clinics, according to the surgeons.

Known in the West as 'Valentine anguloplasty' after the heart shape of the removed muscle tissues at the lip's edge, the smile surgery was first developed as a part of an overall anti-aging face lift, Dr. Kwon and other surgeons say. Tightening the drooping face parts didn't restore the lips to the original upturned position, making an extra procedure necessary, they said.

'It is going against gravity, ' said Dr. David Song of Golden View Plastic Surgery. He added that he observes the patient in different poses, such as in a seated position or while lying down, to get the most natural angle for the lips. 'We're restoring the original lip line.'

Though South Koreans are some of the most avid users of plastic surgery in the world - the country has the world's highest number of cosmetic surgery procedures per capita, according to the International Society of Aesthetic Plastic Surgeons - the area around the mouth was relatively unexplored, the surgeons say.

The age demographic of clients asking about the smile surgery became substantially younger, the surgeons say, after some celebrities' smiles began attracting public scrutiny earlier this year. Few have admitted to going under the knife for a perkier expressions.

But some clinics now publicize more than 15 different procedures for the lip and the mouth, including enlargement, reduction and gum exposure reduction. The most common procedure? The smile surgery, according to Dr. Cha Seung-youn at ZIEN Plastic Surgery.

'Your eyes and mouth make up the most of your facial expression, ' said Dr. Cha.

With a typical price tag of up to $2, 000, the 'natural' killer smile doesn't come cheap, and Dr. Song warns that consistent care will be needed over a three-to-six months of the recovery period.