Shocking images show how a woman was left with a gaping wound on her head after getting her hair coloured at a salon.
The unnamed 21-year-old, from Seoul, South Korea, visited her local salon to get her hair lightened.
But, instead of giving her the colour she desired, the chemicals in the dye caused a deep open burn across the length of her head and made her hair fall out.
Doctors say she was exposed to persulfates and hydrogen peroxide - two potent chemicals found in dye - for too long.
The chemicals are the active ingredients in most highlighting products on the UK high street.
Doctors wrote about the incident in the journal Archives of Plastic Surgery, led by Dr Suk Joon Oh from the Department of Burn Reconstructive Surgery at Bestian Seoul Hospital.
The patient was treated with a mainstream colouring product in her local salon. The doctors don't reveal the name of the product or how it was used.
But they suggest 'prolonged exposure' to the mixture may have caused the traumatising wounds, potentially because they contained particularly potent chemicals.
The doctors explained that the two of the chemicals - ammonium and potassium persulfates - are acidic and flammable.
And the dye contained hydrogen peroxide, a powerful chemical which can be found in high concentrations in hair formulas.
Dr Oh said: '[Hydrogen peroxide] is a clean, colorless, non-flammable liquid and is not well absorbed through intact skin.
'At the concentrations used for household sterilization purposes, three to five per cent, it is slightly irritating to the skin.'
But at the concentration of 10 per cent that is found in many hair colouring materials, it is highly irritating and corrosive, and can therefore lead to skin blisters and burns, Dr Oh said.
Hair dye formulations can contain a very high concentration of sulfates of up to 60 per cent.
In the UK, the maximum concentration of hydrogen peroxide allowed for use in hair products is 12 per cent. Persulfates do not have any specified concentration and hair lightening products may contain up concentrations up to 70 per cent, according to the Cosmetic, Toiletry and Perfumery Association (CTPA).
Over a prolonged time, a high-energy reaction, caused when the chemicals come in contact with skin tissue, can destroy human flesh.
This resulted in flesh on the woman's scalp dying during process called coagulative necrosis, which is a form of cell death triggered by a lack of blood supply.
Dr Oh said: 'Coagulation necrosis is caused by direct contact between the oxidising salt and the tissue.'
He continued: 'As clinicians, we must educate people about the risk of burns caused by mixtures used for hair colouring, provide information on the safe use of these compounds, and join in current efforts to ban these chemicals from hair coloring products.'
The patient had a hair follicle transplantation afterwards, with images showing her hair's recovery in the months after the event.
Dr Greg Willliams, a leading UK plastic surgeon in burn scar alopecia at the Farjo Hair Institute, said: 'Incidents like this can be extremely traumatic for the patient.
'The hair loss can have an equal or greater impact on the self-esteem and quality of life of patients than the scars themselves and act as a constant reminder of the causative traumatic incident.'
The woman's hair was replaced using a 'follicular extraction method' transplant, available in the UK, which uses natural hair follicles from the patient.
Dr Williams, a former clinical director of the London's Burn Centre at the Chelsea and Westminster Hospital NHS Foundation Trust, said: 'Thankfully, technological advances now mean that it is possible to restore hair where it has been lost due to burns scars.'
Hair restoration on tissue once damaged by burns is complex and can take longer to achieve than typical hair transplant surgery.
Dr Bessam Farjo, founder and director of the Farjo Hair Institute clinics in Manchester and London, said: 'With a hair transplant, we move follicles from a donor site which is usually at the back or sides of the head to the affected scarred area.
'But the ability of the graft to take hold and thrive is not as reliable as it is in healthy non-scarred skin and may need repeating to achieve adequate density, which is important for a natural look.'
The surgeons see many people who suffer extreme hair dye burns who need transplants to correct the bald areas left behind.
Hair lightening products containing persulfates and hydrogen peroxide are permitted for use in the EU and UK only after being thoroughly checked for safety.
Dr Emma Meredith, a pharmacist and director at CTPA said: 'Cosmetic products, including hair lightening products, are covered by robust, strict legislation, the EU Cosmetic Products Regulation 1223/2009 (CPR).
'They are safe for use, provided of course the instructions for use are followed.'
Typically a salon would leave hair dye on for 30-45 minutes maximum, and 'box dyes' bought in stores vary.
A BBC investigation in 2017 warned many clinics don't abide by industry guidelines stating hair dyes shouldn't be used on under-16s.
Some components in hair dyes can cause symptoms of an allergic reaction, which is why manufacturers say a skin tolerance test must be carried out 48 hours before - for both home dye kits and those used by professionals in hair salons.
Most commonly the chemical paraphenylenediamine (PPD) causes reactions from mild skin irritation to swelling.
In November, teenager Riley O'Brien was temporarily blinded for two days and left with pus-filled scabs on her hairline after suffering an allergic reaction to hair dye.
The 18-year-old, from Colchester, used a cream-based permanent dye in dark brown but was left with chemical burns and a swollen face.
Reactions to PPD can range from mild irritation in the scalp to an allergic reaction that can potentially trigger serious symptoms throughout the body.
Source: The Daily Mail