"One hundred percent of women who come here have it done," she said. "People think it's prettier to look white. In my opinion, dark is prettier. I don't know who they want to look like."

In many countries in Africa, the Middle East and Asia lighter-coloured skin is considered prettier and paler women are believed to be wealthier, more educated and more desirable.

This attitude has led to a boom in the use of skin-lightening products in Sudan, a vast country torn by war where skin colour also has political connotations.

Rasha Moussa, a maid, pulls some skin-whitening cream from her handbag.

"I use it on my face to make my face shine. The Sudanese see the light colour as better than dark. I think it's a complex that we have," she said.

"People judge you here by your colour ... If they see me and someone else with lighter skin wearing the same clothes, they would say she is living a comfortable life and I'm a poor woman," she added.

Millions of women throughout Africa use creams and soaps containing chemicals, like hydroquinone, to lighten the colour of their skin. But the creams can cause long-term damage.

Dermatologists say prolonged use of hydroquinone and mercury-based products, also found in some creams, destroys the skin's protective outer layer. Eventually the skin starts to burn, itch or blister, becomes extremely sensitive to sunlight and then turns even blacker than before.

Prolonged use can damage the nerves or even lead to kidney failure or skin cancer and so prove fatal.

"It's a very bad problem here. It sometimes kills the patient ... It's bad, bad news," said a doctor at a Khartoum hospital. He said the number of women coming to the dermatology department with problems caused by skin-whitening treatments had grown to at least one in four of all dermatology patients.

In Khartoum, skin-whitening creams are displayed prominently in stores and on roadside adverts. Products advertised on Arab television channels promise the creams will also make a woman more confident and glamorous.

In one advert, a previously unremarkable female television presenter delivers a stunning report after using whitening cream. Her handsome male colleague, who has previously ignored her, says: "You were great. What are you doing at four?"

In another, a singer leaves the stage with stage fright but returns after lightening her skin and performs wonderfully.

At the Modern Style bridal store, an array of skin-whitening creams adorn the front desk. Next door, a photography studio displays wedding portraits of women with very pale skin.

Modern Style's Egyptian owner Samira Magar tied the growing preference for white wedding dresses, which are not traditional in Sudan, to the desire for pale skin.

"More Sudanese are getting white wedding dresses, so they want to look like Egyptians and Europeans," she said.

"I think it's an inferiority complex. They think that if they're white in colour, they are more beautiful," she added.

Magar said some women had resorted to mercury and harsh prescription creams not meant for cosmetic use, leaving their faces disfigured on their wedding day.

Natural methods of skin whitening have been used for centuries, Magar said, but in Sudan the use of chemicals began in the 1980s and has thrived since.

The doctor at the Khartoum hospital, who declined to be named, said the creams now used can cause irritation and infection, blotching, eczema, and that most contain steroids.

The doctor said that rather than ask why women use the creams, men should be asked why they prefer pale skin.

"Here, all men want to sit with or marry a woman with light skin. If any man wants to marry, he says the first choice is for a woman with light skin ... Why is this?"

While a tan can be seen as something of a status symbol in the West, darker skin marks out women in Africa, the Middle East and Asia as poorer people who have no choice but to toil under the hot sun.

In Sudan, Africa's biggest country, over two decades of civil war between lighter-skinned northerners and darker southerners has given skin tone more sinister connotations, and the meaning of the various shades is nuanced.

Northerners, who are mainly Muslims and claim Arab lineage, have traditionally held power. A north-south coalition government now shares power after a peace deal last year.

During civil strife, skin tone often meant the difference between life and death. Southerners, traditionally Christian or animist, complain of prejudice against them in everyday life, and some northerners privately claim superiority over their darker and non-Arab countrymen.