Trading standards officers in Liverpool have seized more than 4,000 fake GHD hair straighteners in the past year.
The imitations of the popular brand are defective and can catch fire, causing burns or electrocution, they have warned.
Consumers are being urged to avoid buying cheap versions of the product, which are often sold on websites for about £30.
The genuine items retail for between £90 and £110 on the high street.
Some of the fake GHDs seized in Liverpool have faulty wiring and were found to melt the plastic around the ceramic plates, said Keith Marshall, of the city's Trading Standards team.
"If you're unfortunate enough to actually be using these, you're going to be dragging these through your hair and this molten plastic will not only get tangled in your hair, but drop onto your scalp causing serious burns and injury," he said.