Second Hand September is a campaign encouraging people to avoid buying new clothing for the entire 30 days of the month.
The campaign, organised by the charity Oxfam, aims to raise awareness of the environmental impact of fashion.
Currently, almost 1.2 billion tonnes of carbon emissions are produced by the fashion industry and 11 million items of clothing are sent to landfill every week in the UK.
It's not the only campaign asking for people to stop buying new clothing. Extinction Rebellion recently asked its followers to boycott fashion for a year, and requested that London fashion week be cancelled.
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In the UK we buy twice as many new clothes as we did a decade ago. It's far more than any other European countries.
Lots of the clothes we buy are made on the other side of the world and they are imported over. This means the fashion industry creates a massive carbon footprint.
The imported clothing is often very cheap. It is known as 'fast fashion'.
'Fast fashion' is the name given to how quickly people buy and chuck away clothes nowadays. Sometimes, people only wear garments once before discarding them.
Currently, less than 1% of the material used to make clothes is being recycled into new garments when the clothes are no longer wanted.
The House of Commons Environmental Audit Committee says there is a basic problem with an industry that relies on persuading people to throw away good clothes because they are "last year's colour".
According to Oxfam, if everyone in the UK took part in Second Hand September the country would save the same amount of emissions as flying a plane around the world 900 times.
"These staggering facts about fashion's impact on the planet and the world's poorest people should make us all think twice before buying something new to wear," Oxfam chief executive Danny Sriskandarajah said.