Concerned consumers can take personal action to avoid buying new plastic and still dress up for Halloween.
Halloween costumes sold by some of the UK's biggest retailers will contain the equivalent of 83 million plastic bottles, a study suggests.
A staggering 83 percent of the material in the costumes is oil-based plastic, an investigation of 324 clothing lines sold by 19 retailers by the environmental charity Hubbub and nature charity The Fairyland Trust found.
The most common plastic polymer found in the clothing sampled was polyester, making up 69 percent of the total of all materials. The study predicts that the costumes will add up to 2,000 tonnes of plastic waste in the UK this year.
Both charities are urging families to avoid adding to problems caused by plastic waste by creating their own costumes from existing or second-hand clothing.
They are also calling on manufacturers and retailers to rethink product ranges for seasonal celebrations and for better and consistent labelling to help customers choose environmentally-friendly options, saying they believe many shoppers do not realise that materials like polyester are in fact plastic.
Chris Rose, from the Fairyland Trust, said: "The scariest thing about Halloween is now plastic. More costumes are being bought each year as the number of people participating in Halloween increases.
"Research by Hubbub estimated that 33 million people dressed up for Halloween in 2017 and a shocking four in 10 costumes were worn only once. This means it's vital that we all try and choose costumes that are as environmentally friendly as possible.
"Concerned consumers can take personal action to avoid buying new plastic and still dress up for Halloween by buying from charity shops or reusing costumes to create outfits, or making their own from non-plastic materials."
Trewin Restorick, chief executive of Hubbub, which is working with the all-party parliamentary group looking into the environmental sustainability of the fashion industry, said: "The amount of plastic waste from Halloween costumes is similar to the weight of plastic waste generated at Easter in egg-wrappings.
"However, the total plastic waste footprint of Halloween will be even higher once you take into account other Halloween plastic such as party kits and decorations, much of which are also plastic, or Halloween food packaging, most of which quickly becomes rubbish and, ultimately, breaks down to be plastic pollution.
"Retailers must take greater responsibility to offer ranges for seasonal celebrations that don't worsen the already worrying impact of plastic waste on our planet."
Paula Chin, sustainable materials specialist at WWF, said: "There is nothing scarier than our throwaway culture.
"By reducing the amount of plastic we buy, embracing reusable items and taking responsibility for our waste, we can make sure Halloween is suitably spooky and sustainable."
Josie Clarke is a consumer correspondent with PA.