Dr Victor Lui Wing-cheong, vice-chairman of the Consumer Council’s research and testing committee, said in an online press briefing on Monday that due to the ongoing coronavirus pandemic, more people were opting to do at-home hair treatments, particularly with brands featuring “natural” claims, assuming those products were less likely to cause a reaction or damage their hair.

“As chemicals in permanent hair dyes open up the cuticles of the hair to allow the dyes to enter the [scalp], these chemicals may induce allergic reactions and damage the hair surface, resulting in dry or frizzy hair,” said Lui.

While no extreme allergic reactions were reported related to hair colouring products last year, the council received four complaints demanding refunds after users experienced skin irritation when using such products.

The watchdog’s chief executive, Gilly Wong Fung-han, said the only naturally occurring ingredients found in the products were plant-based pigments such as indigo and henna powder.

“Henna has to be applied on hair for at least three to five hours before it can show a dyeing effect,” Wong said. “Because of the long duration it takes for hair dyeing, many manufacturers will add some chemical substances to improve the colouring effect and also to shorten [the time it takes].”

The Consumer Council’s test found allergens such as p-Phenylenediamine (PPD), m-Phenylenediamine (MPD) and Toluene-2,5-diamine (PTD) in the hair products.

PPD, a common component in hair dyes, should not exceed concentrations of 2 per cent, according to cosmetic regulations in the European Union and mainland China.

However, the watchdog found that two henna-based hair dyes – Herbul Black Henna Dye and Melva’s Hair Colour Powder with Natural Nourishing Herbs – both exceeded that limit, containing 8.4 per cent and 4.2 per cent PPD, respectively. Both of the products were made in India. Korean-made Cosline’s Squid Ink Speedy Color Cream (1N) was right at the upper limit, with 2 per cent of the ingredient.

One mutagenic ingredient prohibited by both EU and mainland cosmetics regulations was also found in one of the products called TS Chakhan Hair Color Cream.

Meanwhile, all six henna hair dyes were found to contain levels of lead ranging from 0.04 to 3.1 parts per million. One of the products was found to contain a concentration of mercury of 0.043 parts per million.

While the heavy metal contents of the samples were within mainland Chinese standards – which allow for up to 10 parts per million of lead or one part per million of mercury – the watchdog cautioned that prolonged exposure posed poisoning risks.

The study also found that five of the hair colouring products did not list the ammonia content, and two of them – Herbatint and Tints of Nature – even claimed to be “ammonia free” when they actually contained the chemical. Both of those products were less than 0.02 per cent ammonia.

Among the products tested, 17 had a full list of ingredients, seven only had a partial list and two did not have any information on their contents at all.

The ingredient-labelling issues have been referred to the Customs and Excise Department.

The council reminded consumers to conduct a skin allergy test according to the product’s instructions before using the dye on their hair. Those with eczema or scalp damage should also avoid hair dye treatments.

The watchdog also noted that based on current scientific research, those with favism, an allergy to fava beans caused by a Glucose-6-Phosphate Dehydrogenase (G6PD) deficiency, should not use henna due to the risk of adverse reactions.