42 TESTING
and the oxidation of dihydroxyphenylalanine (DOPA) to melanin. Byproduct reactive oxygen species (ROS) induced during melanin biosynthesis have a detrimental effect upon both melanocytes and upon melanosomes transfer into keratinocytes. At the same time, with ageing, there is a decline in the ROS scavenging and damage repairs abilities which are supposed to counteract oxidative stress. Risk factors associated with canities include some auto- immune disorders but also external factors such as nutritional deficiencies. The roles of genes in human hair greying is still poorly understood but heredity is likely to play a role.3,4
Hiding or reversing hair greying The English writer P.G. Wodehouse wrote ‘There is only one cure for grey hair. It was invented by a Frenchman. It is called the guillotine’. As one of the author of this paper is French, we feel obliged to disagree with this very strong statement. At least partially, because it is true that hair greying was believed during a long time to be an irreversible process. More seriously, because of this belief in the
impossibility to reverse the natural course of hair greying, hair dyes were – and mainly are still – the only solutions to bring back the native colour of hair.5
Natural dyes such as henna were
a traditional option although henna typically provides reddish or orange hues on grey hair. Other natural dyes can offer brown or black
hues. Hair dyes come in various types, each with different characteristics and purposes. Permanent hair dye contains chemicals that penetrate the hair shaft and are then oxidized by hydrogen peroxide to activate the colour change.
The advantage of permanent dyes lies in the
long-lasting effect and its resistance to normal hair washing. Semi-permanent hair dyes are small molecules that penetrate the cuticle, adding colour to the outer layer of the hair, but gradually fading until disappearance after four to 12 shampoos. Finally, temporary hair dyes consist of
large complex organic structures that do not penetrate the cuticle, therefore providing a short-term colour change which often lasts until the next shampoo only. Semi-permanent and temporary dyes are gentler for the scalp and hair but their camouflage effect is inferior to that of permanent colourants. In the medical field, a growing number
of grey hair repigmentation cases have been reported following diverse pharmacological interventions, thus challenging the notion of hair greying irreversibility.1,2
Many case reports
originated from the observation of ‘side effects’ of anti-inflammatory, chemotherapy treatments for instance. Due to the nature of these molecules, their
cosmetic use for darkening hair is excluded but understanding their mechanisms of actions could well open, one day, the way to new hair repigmenting actives. Theoretically, hair greying could be prevented if ROS are adequately removed by effective antioxidants. So deciphering the susceptibility of melanocytes to oxidative stress might yield clues to possible
PERSONAL CARE November 2024 C D Figure 2: (A and C) Clinical photograph demonstrating a 1 cm2
treatments for the prevention and reversal of canities. In recent years, an increasing number of
anti-grey hair treatments aiming at preventing or reversing canities have entered the market. Many are based on herbal extracts or blends of vitamins, B12 being especially popular. As for today, there is limited scientific evidence that certain treatments can actually reverse hair greying. This lack of proof pleads for the need for rigorous evaluation of the efficacy of anti- canities interventions.
In vivo assessment of interventions in hair greying Publications about substantiation of cosmetic and pharmacologic interventions for canities are very scarce. There is no method universally adopted by the personal care industry. Here we will present a selection of the most common available techniques and will discuss their main advantages and shortcomings. The easiest method relies on self-
assessment based on questionnaires. This is very simple, suffers from its subjectivity by definition, but has nevertheless some interest when performed on a population large enough since results are a reflection of the perception of consumers. Slightly less subjective is self-grading where
subjects rate different hair descriptors by using visual analogue scales (VAS) for example. It typically consists in marking a point on a line with endpoints defining the extremes, from 1 (all hair pigmented) to 10 (all hair white), for instance.
The distance from the minimum to the mark provides a quantitative score. VAS is valued for
area and clipped to approximately 1 mm
above the scalp surface (B and D). Magnified view of the photograph (white and black dots represent grey and black hair, respectively). Reproduced from Singal et al
its ease to use, making it a popular choice in cosmetic/dermatologic research settings. When the grading is done by trained evaluators or by dermatologists, a more objective assessment can be achieved. Different specific scales have been used.
Recently a study was based on the assessment of the proportion of grey hair (scale from 0% to 100%) determined by the blind scoring of photographs taken at baseline and Tn.6
As an
attempt to standardize and achieve objective and reproducible means of assessing the severity of the greying of hair, the Greying Severity Score (GSS) has been proposed.7 The GSS requires the acquisition of photographs of five scalp areas of 1 cm2
taken
on the vertex, right and left temporal, frontal and occipital regions. A score is then allocated to each region based on the computer-assisted counting the numbers of grey and coloured hairs by experts (Figure 2). Finally a cumulated score is calculated. The main limitation of this scoring system, according to the authors themselves, is its time-consuming nature. Although a score if the final outcome of the above GSS, the method is actually a combination of digital photography/ image processing and clinical scoring. This leads us naturally to the more objective and quantitative instrumental and photographic methods. What comes to mind first when we are
interested in the instrumental measurement of hair colour are chromametry and spectrophotometry. Indeed, many laboratories have used these gold standard techniques, either for fundamental studies of the diversity of the natural colour of the human male and
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