Many people may take their birth certificate, or similar official papers, for granted - hidden in a drawer and rarely seeing the light of day - but for those without one, it can lead to a shadow life or an uncertain existence.

This is thought to affect millions of people around the world, described as stateless, and 25-year-old South African Arnold Ncube is one of those.

Because he has no state-issued documents, washing cars in the backstreets of Thembisa township near Johannesburg is one of the few ways he can make a living.

He was born in Johannesburg and his father is South African, qualifying him for citizenship here. But when he tried to register for secondary school, he realised he didn't have a birth certificate.

Having been abandoned by his parents - his dad left before he was born and his mum when he was 14 - he could not prove his status.

It's a painful thing, he says. You're basically invisible. You don't exist. It's like you're living in the shadows. You don't have a bank account, you can't apply for a decent job that you can earn a living with.

He adds that he tries to stay positive but it's been challenging.

When I see my peers, they are done with school now. Whereas I couldn't study further. It's a lot. Depression was once my friend.

Arnold is one of at least an estimated 10,000 stateless people living in South Africa who, despite being born here, are struggling to prove their nationality and access public services.

With no citizenship, stateless people cannot get documents and struggle to get access to basic necessities including education and healthcare.

Statelessness is caused by many factors, including administrative barriers and poor record-keeping. As a result the real number of stateless people is hard to gauge in many parts of the world.

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Statelessness is not just an issue here; it is a huge global problem. Experts believe tackling the problem requires policy changes, including allowing refugees to register their children where they're born, and giving mothers the right to pass their nationality to their children.