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have been known for decades. Some of these “classical methods” have also been used on hair and scalp for quite a while.
Sebum on hair & scalp The sebum for hair and scalp is produced by the sebaceous glands on the scalp. The sebum gland releases the oil to the hair via a small channel. It is then transported along the hair shaft away from the scalp. The main task of the sebum is to protect the scalp and to keep the hair shiny and supple while preventing it from breaking. When produced in a high quantity, sebum
leads to greasy hair and scalp problems that may cause increased microbial activity and oily dandruff. Especially in urban areas with high pollution, fine dust particles and other pollutants may cling to the oil, making the hair look dull and degrading the hair quality. To remove the oil and pollutants, frequent washing is required which will most notably dry out longer hair. Also, this might just trigger the production of more oil to compensate for the frequent removal – leading to a vicious circle. So, the aim would be to balance the oil production to a moderate level or develop products with lipid-restoring properties. The Sebumeter® for example is not only the
world’s most used instrument to determine the sebum content of the skin but already in the 1980s and the early 90s, work has been presented about the usefulness of this device on hair and scalp.7,8 For optimal reaching of the hairy scalp, a special adapter can be useful to measure with the milky foil of the Sebumeter® that will become transparent when absorbing the oil. After the foil has been removed from the scalp, its transparency is evaluated photometrically.
Hair colour and gloss are “evergreens” among the claims around hair care Easy and quick to use. Colorimeter and Glossymeter devices which have been used on skin for a long time and are also suitable to support the booming claims like brightening, luminosity, shine, colour intensity/lasting for hair.
Hydration Hydration on hair is more difficult to measure than on skin. However, dehydrated hair is one of the main consumer concerns9
Figure 4: pH-measurement on hair and scalp. with regards to hair care.
One method that has been used to determine the moisture content of hair is the measurement of induced chemoluminescence. However, this method requires a huge financial and spatial expenditure. A promising approach has been tested by Pierard et al. using capacitance imaging.10 The MoistureMap device using this method could become an interesting tool for such tests. The pH-value on hair and scalp plays an
important role in the efficacy testing of hair care. Claims like “pH-neutral” or “sensitive” are easy to support by pH-measurements.
Product safety The barrier function of the scalp is the key parameter in the safety and efficacy evaluation of products applied on the head. Since the ban of animal testing in the development of cosmetic products, TEWL measurements have to take place in vivo on human subjects and in vitro on cultured
PERSONAL CARE March 2021
cell tissue. The open chamber measurement of the Tewameter® is the world’s most-used method for the assessment of transepidermal water loss (TEWL). The Tewameter® Nano probe has been developed to especially measure the scalp. With its small measurement surface of only 2 mm diameter, the scalp can easily be reached through the hair. TEWL measurements are also used as indirect measurements of the water content on the scalp.
Imaging Following the tendency in evaluating skin care efficacy and its claim support, also in hair care development more and more methods are based on image analysis. The evaluation of the hair length can be
used for different claims. In hair care and food/ food supplements hair length assessment can substantiate hair growth claims. Also, in testing the quality of shaving, this measurement will be useful. Thickness measurement of the single hair are used to show the volumizing effect of products. Special UV-based cameras such as the
Visioscan® offer high resolution, non-glossy images of hair and scalp. Other cameras with parallel – and cross-polarized light show scalp and hair images from different angles. Other methods such as transmitted light
Figure 5: Tewameter® Nano, especially developed for TEWL measurements on small and difficult to reach surfaces.
microscopy, scanning electron microscopy (SEM) but also high resolution-cameras with magnification objective can show structural hair fibre damage and substantiate hair repair claims.
Dandruff The same way as skin does, the scalp will constantly shed small dandruff flakes from its surface. This is a normal process making room for new cells growing from the base of the epidermis. Usually, these minuscule and more or less imperceptible flakes will be removed by washing and combing the hair. However, almost 50% of the world’s population show plainly visible flakes at one time or another, a problem described as dandruff.11
In general, dandruff causes more social
and psychological problems than medical ones, effecting self-esteem and confidence. 12 Dandruff is difficult to define because it can
manifest in different conditions and blurs with seborrhoeic dermatitis and other scaly skin problems such as atopic dermatitis and psoriasis.13 It is often linked to the colonisation of the scalp by Malassezia, a fungal microorganism. Also, seborrhoeic conditions, allergies or dehydration of the scalp may result in dandruff. Additionally, external triggers have been identified, such as sun exposure12
or treatment with unsuitable products.
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Figure 3: Glossymeter and Colorimeter probes can be used in vivo and in vitro.
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