Q & A

Despite widespread bans on hydroquinone, skin lightening is a global epidemicA widespread disease or infection. and it's spreading. The value of the industry is expected to soar to $31.2 billion (£25 billion) by 2024.

Why are people risking their health to bleach their skin? The problem, commentators say, is colourism - a type of racism that discriminates based on skin tone, with light favoured over dark.

Khoudia Diop knows the harmful effects of colourism first-hand. Growing up in SenegalA country in west Africa with a population of 17 million. , she was constantly bullied for her dark skin.

"At first, I tried confronting them, but soon I learned to tune out the negativity," she says.

Half of women in Senegal bleach their skin. That figure is 77% in Nigeria, and 40% in China. The biggest market for skin-lightening products is Asia, where colourism is driven by a toxic mix of British colonialismThis refers not only to the material realities of colonial rule, but also to the mindset of the colonising powers and their ways of justifying empire. Most Europeans believed that empire was a moral good, because it imparted 'civilisation' to 'primitive' cultures and so helped them to develop. and class discrimination.

Today, Diop is a full-time model and a champion of the fight against colourism. Since her striking modelling shots went viral, Diop's Instagram account, the "Melaniinn Goddess", has gained over half a million followers. After years of bullying, the 22-year-old is proud of her skin tone.

"Diversity is what makes life interesting. All women should feel confident in the skin they're in - everyone is beautiful in their own unique way," she says.

But studies show there is still a long way to go.

While light-skinned actors and musicians rise to the top of the entertainment industry, those with dark skin say they are languishing on the sidelines.

According to science journalist Shankar Vedantam, dark-skinned HispanicRefers to peoples, countries or cultures linked to Spain. Often used to talk about people from or descended from Latin American countries. Americans earn on average $5,000 (£4,070) a year less than those with fair skin. A Villanova University study of 12,000 African-American female inmates found that women with lighter skin were more likely to get shorter sentences.

The impact of colourism runs through all levels of society. Is this the worst form of racism?

For author and journalist Poorna Bell, colourism is a "poison" that runs through families and communities. It is "fed to you from the moment you are born, continues to be administered as you grow up, and taints the entire foundation of your self-worth as an adult". Because it is more subtle than all-out racism, the malignantUsed to describe something which is hostile or very invasive. It is often used to describe disease, especially cancer. influence of colourism has spread widely and deep.

But, ultimately, dark-skinned people are experiencing an exaggerated form of the racism still faced by people of colour across society. In the USA, just 43% of Black families own a home, compared to 73% of White families. In the UK, ethnic minorities are twice as likely as White people to have been overlooked for a promotion at work. Colourism is an extension of a wider, lingering racism.

What do we know? Khoudia Diop is a 22-year-old model and actress from Senegal. In 2016, a photograph of Diop that was taken for a project with The Colored Girl diversity campaign went viral. Overnight, her Instagram followers soared from 300 followers to 350,000. Now, she has more than half a million, and works full-time as a model.

What do we not know? How long it will take to rid society of colourism. As a form of prejudice, it has a long and unpleasant history. In the USA, colourism emerged from slavery, as masters favoured lighter-skinned slaves, who were sometimes the children of slaves raped by White masters. Well into the 20th Century, Black applicants would list "light-skinned" as a qualification when seeking employment.