Halloween revellers are being warned about the dangers of "spooky" contact lenses.
The coloured cosmetic lenses are often illegally sold online, in shops and on market stalls, rather than by a registered optician or doctor.
Experts said people could suffer vision loss or infection from the lenses, with an increased risk for those who share them with friends, wear the same pair year after year or store them in water.
Badrul Hussain, consultant ophthalmic surgeon at Moorfields Eye Hospital NHS Foundation Trust in London, said: "Each year we treat patients, including children under 16, who have developed eye conditions after wearing cosmetic contact lenses.
"There can be an increase in these problems in the period around Halloween.
"The cornea, the clear window at the front of the eye, is delicate and can be scratched easily by inexperienced contact lens wearers.
"This can expose the eye to organisms that can cause nasty infections, which in extreme cases can result in permanently impaired, or loss of, vision."
The warning comes as it was revealed an estimated seven million Halloween costumes ended up in the bin last year, contributing to the 300,000 tonnes of clothing sent to landfill annually.
Just over half of UK households have at least one person who gets dressed up, but each costume is worn only twice on average and 37% are worn just once, according to the survey for environmental charity Hubbub.
The charity has teamed up with the North London Waste Authority to launch the SewSpooky campaign to encourage more people to make costumes from household materials and pass on their used outfits to friends and family for future wearing.
The survey found that the average spent on each Halloween costume last year was £15.56 and politicians and film characters are a popular choice of costume for adults, with last year seeing 1.4 million Donald Trumps.