Assessing the dyeing efficiency and irritation potentials of plant hair dyes: A multi‐analytical in vitro approach

Abstract

Background:The interest toward dyeing hairs with plant colorants has grown in popularity considering its low-toxic nature. However, researches reporting plant hair dyes are limited and the potential adverse effects of irritation are unclear.Objectives: This study is aimed to provide an avenue by which to more accurately assess the dyeing efficiency and irritation potentials of plant hair dyes. Methods: Four extracted plant colorants were incorporated in hydrogel hair dyes that were directly applied on unbleached gray human hairs. Their dyeing performances and the effect of an iron (Ⅱ) mordant were photometrically measured in CIELab coordinates and color strength. The eye and skin irritancy was assessed by combining various in vitro methods, including bovine corneal opacity and permeability (BCOP) assay in combination with histopathological analysis, Hen's egg test on chick chorioallantoic membrane (HET-CAM) and a test on reconstructed human epidermis models. Results: The investigated hair dyes exhibited desirable dyeing efficiency on human hairs. Post-treatment with the iron (Ⅱ) mordant caused a significant increase in color strength with subtle changes to the hue of dyed color. In the irritation testing, the four hair dyes were categorized as slight-to-mild eye irritants but possessed no skin irritation potential, while the mordant was determined as a non-irritant. Conclusions: The results demonstrate the efficacy of a multi-analytical approach for in vitro assessment of various plant colorants for hair dyeing. The investigated plant extracts are suitable for producing viable colors on human hairs and may serve as a low-irritating alternative to the synthetic hair dyes. K E Y W O R D S hair coloring, hydrogel, in vitro, irritation, plant hair dyes | 1565 TANG eT Al.

Stabilisation and detoxification of henna (Lawsonia inermis L.) extract for hair dye cosmetics by spray‐drying encapsulation

“…A pronounced darkening effect, demonstrated as enhanced colour difference (∆ E ) between the dyed and undyed hairs (Table ) and enhanced K / S (Figure A), was evident in all hair samples which had been post‐mordanted with ferrous sulphate. These observations show that the ferrous ions are able to form iron complex chromophores with the henna dyes and hair fibres resulting in subtle colour changes to the colour of dyed hair mordanted with ferrous ions . As shown in Figure , the maximum K / S of ferrous‐mordanted hairs redshifted to longer wavelengths, resulting in a colour change from yellowish orange to reddish brown, which is consistent with our previous results obtained on human hair dyed with a hydrogel formulation containing henna extract .…”

“…The major colouring compound, lawsone, in HE and HM, was quantified by HPLC using a Shimadzu LC‐20AD pump associated with an Ultimate Plus C18 column (150 mm × 4.6 mm, 5 μm) . The mobile phases were a 30:70 (v/v) mixture of methanol and 0.1 mol L −1 acetic acid solution.…”

“…The colours of HE or HM powders as well as the dyed hair fibres were measured in CIELab parameters ( L* , a *, b* ) by using a NH310 colorimeter (Shenzhen 3nh Technology) under D65 illuminant (10° observer). Powder or hair fibre samples were placed into a specially designed quartz sample holder to ensure sufficient thickness and a smooth surface, as required for the colour measurement …”

“…Each endpoint was graded from 0‐3 according to the severity of the vascular response, and an S (severity) score was calculated. The eye irritancy was categorised according to the criteria: severe irritant (S ≥ 15), moderate irritant (12 ≤ S < 15), mild irritant (6 ≤ S < 12) and non‐irritant (S < 6).…”

“…There are numerous reports of research into its extraction and application in textile fibres and increasing efforts are being made to improve its colour strength and fastness properties, such as by alkaline extraction and treatment with metallic salt mordants (eg, ferrous sulphate and potash alum) . Similarly, in our previous study, a hydrogel formulation prepared from henna extract in combination with a ferrous sulphate mordant produced enhanced colour strength in human grey hairs compared with dyeing without mordants …”