When Lego started testing a service to receive and re-use second-hand bricks, the Danish toymaker soon ran into a problem: people would send in other things as well. Soda cans, shoes, lots of hair — all came mingled in with the iconic plastic bricks, according to a senior executive.

Worst of all: workers once opened a Lego treasure chest to find an entire set of children’s teeth in it.

Brands from Shein and Zara to H&M and Lego are throwing themselves into a booming second-hand economy. They are joining a growing number of start-ups such as Vinted, Depop, ThredUp, and Vestiaire Collective in attempting to make money from a rush to embrace used and “preloved” items, whether due to cost or environmental concerns. Celebrities such as Bella Hadid, Rihanna and Sarah Jessica Parker have all embraced thrift as has even cult TV show Love Island.