Young people are putting their sight at risk by sharing coloured contact lenses, UK experts warn.
The General Optical Council said the cosmetic lenses, which change eye colour and have been made popular by TV programs such as the Vampire Diaries and Twilight, were being shared between friends, increasing the risk of corneal ulcers and infections.
Cosmetic coloured lenses are available online and are also sold on market stalls and in some shops.
The law states that the contact lenses must be dispensed in the presence of an optician or medical practitioner.
Alistair Bridge, director of strategy at the General Optical Council, said: "Cosmetic contact lenses should not be supplied by anyone other than an optician or doctor. Opticians make sure that contact lenses fit properly and that wearers receive expert advice on how to wear and store them safely.
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"They will also offer important advice such as not to sleep in contact lenses and to never share or swap lenses, which can spread eye disease."
The warning comes ahead of Halloween next weekend, when young people may use the lenses as a way to enhance their outfits.
Leon Livermore, chief executive of the Chartered Trading Standards Institute, said: "Cosmetic contact lenses are often made and distributed on a 'one size fits all' basis and not tailored to the wearer's needs which can increase the risk of eye health issues.
"To minimise these risks, it is essential that cosmetic lenses are fitted by a qualified professional who is able to provide advice on their safe use and ongoing care.
"We would advise against buying products like these online or from retailers as without professional supervision there are more likely to be health concerns for the individual."
The General Optical Council said it had the power to take enforcement action against shops selling the lenses illegally.
