A woman's hair began falling out and her scalp developed scabs after her hair was coloured and straightened at a home salon.
The mishap has prompted warnings for customers to check the qualifications of home salon operators.
The Northland woman, who asked to remain anonymous, said some of her hair fell out after the cut, colour and chemical straightening treatment. She was left with scabs on her head and bald patches, and felt "really sick" afterwards, she said.
The woman opted for the colour and straightening treatments at the same time on the advice of the hairdresser, she said. "We go to home hairdressers all the time. You trust them, you trust the professionals on what they say," she said.
The hairdresser said the customer insisted on getting both treatments in one go, and had an adverse reaction to the chemicals.
"My gut feeling was not to do all the procedures that she wanted done on one day, so I rang my rep, who said it would be fine to do, and obviously she's reacted to the procedure," the hairdresser said.
The hairdresser said she had almost 30 years' experience. The incident was a "human mistake" and she had given the woman a refund.
The New Zealand Association of Registered Hairdressers said it was "not standard practice" for chemical straightening and colouring to be carried out at the same appointment. Vice-chairwoman Yvonne Bowater said she was taught to separate the two chemical procedures by a week.
"It's actually quite stressful on the hair, and the hair needs time to actually come back from that," she said.
"It is not something that we would recommend."
Erica Cumming, chief executive of the Hairdressing Industry Training Organisation, said it was unusual, but some complementary products could be used together.
Ms Cumming said visiting home salons was fine, as long as customers checked hairdressers were registered and qualified.
The hairdresser said she was registered with the local council.
Making the cut
• All hair salons must register with their local council annually, and have a certificate to prove they meet health regulations.
• Salons may also be registered with the New Zealand Association of Registered Hairdressers, which lists registered salons at www.nzhairdressing.org.nz/Salons.
• Hairdressing services are covered by the Consumer Guarantees Act.