South African celebrities are lightening their skin, but in Thailand, they're lightening their genitals too.

There's a clinic in Bangkok that has drawn 100 men a month to its penis-whitening service but social media users are baffled and alarmed by the phallic fad that costs about $650 (R8 000) for five sessions.

The Lelux Hospital, renowned for its body-whitening expertise in a country obsessed with skin colour, began offering the unconventional treatment six months ago after a male customer complained of "dark parts" on his groin.

"These days a lot of people are asking about it. We get around 100 clients a month, three to four clients a day," said Bunthita Wattanasiri, a manager for the Skin and Laser department at Lelux Hospital.

The procedure, which uses laser whitening, got wide play on Thai television and social media after the hospital released images of a man undergoing the treatment.

"We have to be careful because it's a sensitive part of the body," Bunthita said, adding that most clients were aged between 22 and 55 and many were from Thailand's LGBTQ community.

The same hospital stirred controversy last year for touting a cosmetic procedure called a "3D Vagina" in which the customer's own body fat is used to make genitalia more plump.

"I think it's a good market to enter so we offer the ultimate body treatment to our clients, either men and women," Bunthita said.

Whitening and bleaching are not uncommon in other parts of the world and are widely offered online.

But they are particularly sought-after in Thailand, where skin-whitening ads have caused outrage and accusations of racism.

"People nowadays can't embrace their own skin colour," said one Facebook user. Another user, Parin Ruansati, posted: "Oh god... what ever happened to the world?" Another had a lighter response: "Why not?".