Parents desperate to rid their children of headlice are resorting to animal flea treatments available over the counter from vets.
Health authorities have warned against the potentially dangerous practice and urged parents to stick to products made for humans.
An Avondale woman said her sister and sister-in-law had used Frontline
and Spot On on their children after problems with headlice.
Other parents had told the women, who live in Hamilton and Te Aroha, that it was effective and safe.
"My sister did it once and said it works. When you find something that works, it spreads like wildfire."
The woman said she was concerned about how safe the practice was and contacted Occupational Safety and Health, but was told it was not something its staff dealt with.
Waikato medical officer of health Dr Dell Hood said the issue had been raised with her in 1999 and she alerted public health doctors.
She was concerned it was still happening.
"I would warn against it, absolutely. It's dangerous, it's poisonous," Dr Hood said.
"The smaller the child, the bigger the risk."
Manukau vet Steve Merchant said animal flea treatments had not been tested and proven safe on humans.
Frontline was an insecticide and applied in liquid or spray form on an animal's back. It was stored in the sweat glands and excreted for up to eight weeks, preventing flea eggs from producing viable larvae.
"There must be a risk of adverse reactions in people," he said.
National Poisons Centre medical toxicologist Dr Michael Beasley said although some products made for humans contained similar insecticides, they were usually found in much lower concentrations.
The centre had received 24 inquiries over the last two years about animal flea products. Some were general inquiries, some related to use of the product on animals and others to its use on humans.
Five people were reported to have symptoms, including vomiting or diarrhoea, but it was not known if these were linked.
