ABSTRACT
Background:
Correct hair wash frequency and the right product are essential for scalp and hair care. Women wearing hijab are becoming more common. However, no consensus has been published regarding the correct frequency of hair washing, especially for women wearing hijab. Research is needed to compare the influence of different hair wash frequencies on scalp health. The aim of this study is to assess the correlation between hair wash frequency with scalp transepidermal water loss (TEWL) and hydration in women wearing hijab.
Methods:
Sixty healthy women in reproductive age were allocated into 30 subjects in Group A (frequent hair wash, every 1–2 days) and 30 subjects in Group B (infrequent hair wash, every 3–5 days). Measurements of scalp skin TEWL and hydration were performed on baseline, day-14, and day-28.
Results:
The day-28 median value of scalp skin TEWL was 20.87 g/m2/h in Group A and 17.67 g/m2/h in Group B (P < 0.01). The day-28 median value of scalp skin hydration was 11.48 AU in Group A and 12.77 AU in Group B (P > 0.05).
Conclusions:
Frequent hair wash may significantly increase scalp TEWL score in women wearing hijab. However, there is no correlation between hair wash frequency and scalp hydration in women wearing hijab.
Keywords: Hair wash frequency, hydration, scalp, transepidermal water loss, women wearing hijab
INTRODUCTION
Washing hair using shampoo is the most common hair and scalp care practice in the world. Its main purpose is to clean up the hair and scalp from sebum, sweat components, stratum corneum desquamation, hair care products, dust, and dirt.[1] In addition, shampoo is also used to improve hair appearance. Several types of shampoo are available in the market. Shampoo must be chosen accordingly to obtain clean, healthy, and favorable hair and scalp.
In 2010, the Central Agency on Statistics showed that 87.18% of Indonesian residents identify Islam as their religion.[2] One of the fundamental teaching in Islam is the obligatory use of hijab for adult women. The word “hijab” stems from the Arabic term “hajaba” which means “to prevent from seeing.”[3] Recently, the use of hijab has become more common in Indonesian women. Researches on women using hijab are still scarce, however, several literatures stated that the use of hijab may influence scalp characteristic and increase hair loss.[4,5] A case report in India has established the association between hijab usage and the incidence of scalp and hair fungal infection.[6,7]
The most common method to assess skin characteristics is by measuring the skin epidermal barrier function parameters, transepidermal water loss (TEWL), and skin hydration. There is a variety in skin characteristics between men and women.[8] Many literatures have also observed a variety of TEWL and skin hydration values on different anatomical regions, such as the forehead, cheek, and arm. However, measurement of those parameters on the scalp skin is still rare, especially in women wearing hijab.
Besides choosing the right hair care products, to obtain healthy hair and scalp those products must also be used in the correct frequency. Indonesia is a tropical country with high humidity. Usually, the frequency of hair wash that is considered proper in Indonesia is at least once every 3 days.[9] It is believed that using shampoo too frequently or very rarely may influence the physiologic characteristic of the scalp. Aggressive use of shampoo has been observed to increase the risk of skin irritation and contact dermatitis, whereas in African–American race, no correlation has been found between hair wash frequency and hair or scalp disorders.[10,11]
There is no or may be limited literature available that specifically assess the correlation between hair wash frequency and scalp epidermal barrier parameters. Moreover, no general consensus regarding the most correct hair wash frequency has been made, especially in women wearing hijab. The purpose of this study is to assess the correlation between hair wash frequency and scalp TEWL and hydration in women wearing hijab. Ethical Approval for this study was obtained from the Health Research Ethics Committee, Faculty of Medicine, Universitas Indonesia-Cipto Mangunkusumo Hospital (KET-888/UN2.F1/ETIK/PPM.00.02/2019).
RESEARCH METHODS
This is a pilot study designed as a randomized clinical trial, comparing the scalp skin TEWL and hydration values in women wearing hijab who wash their hair once every 1–2 days and every 3–5 days. This study is a part of the main study initiated by the Dermatology and Venereology Department, Faculty of Medicine Universitas Indonesia (FMUI), Dr. Cipto Mangunkusumo National General Hospital (RSCM), titled “Hair and Scalp Characteristics of Women Wearing Hijab Compared with Women Not Wearing Hijab.”
The study was performed from November 2019 to March 2020, at the Department of Dermatology and Venereology FMUI-RSCM and the Clinical Research Supporting Unit of Indonesian Medical Education and Research Institute. The target population was all women wearing hijab, and the accessible population was all women wearing hijab at FMUI and RSCM. Following the recruitment for the main study, subjects participating in this study were determined randomly from subjects wearing hijab.
As a pilot study, the sample size was determined by the researcher. Using the rule of thumb of minimal 12 subjects in every study group, it was decided that the sample size for this study would be 30 subjects in each group.[12] Thus, the total sample size needed for two groups was 60 subjects. Before the initiation of the study, measurements of scalp TEWL and hydration were performed in 10 adult healthy women on different scalp anatomical regions, the frontalis, vertex, and occipital. According to the observation of those three regions, the occipital showed the most consistent results from three times measurements. Therefore, the occipital region was set to be the representative region for the scalp TEWL and hydration measurements in this study.
Prospective subjects that met the inclusion criteria were recruited as the study subjects and were instructed to undergo a 14-day wash-out period. During this period, subjects were instructed to wash their hair once every 3 days using a standard shampoo that was given, while also stopping all types of hair and scalp care products used before. Afterward, baseline data were collected by measuring scalp TEWL and hydration using the Tewameter® TM300 and Corneometer® CM825 devices, produced by Courage and Khazaka Electronic, Germany. Research subjects were also categorized into two groups, Group A (frequent hair wash, every 1–2 days) and Group B (infrequent hair wash, every 3–5 days) using the block randomization method. Subjects were instructed to wash their hair according to their respective group for 28 days. Scalp TEWL and hydration were reevaluated on day-14 and day-28 using the same device and on the same region as before.
The measurements of scalp TEWL and hydration were not performed under direct lamplight or sunlight. The examination room temperature was set to 22°C–24°C and 40%–60% humidity. Subjects were acclimatized for 20–30 min and were in calm and not sweaty condition. Before using the Tewameter® dan Corneometer® devices, hair on the occipital region were combed and clamped with hairpin, then a 1-cm diameter area of hair was cut as short as possible without injuring the scalp.
The tip of the Tewameter® probe to measure TEWL is cylinder-shaped with both sides open (open-chamber measurement). The probe tip must be placed in such a way that one of the open sides of the tip touches the skin surface without pressure and no gap is created. The measurement was started by pressing the button on the lateral side of the probe and pressed again after 30 s to stop it. The measurement was done three times to determine the average value.
For measuring scalp hydration, the Corneometer® probe was placed vertically on the skin surface until the tip was pressed, without excessive pressure. The measurement would start automatically when the pressure on the tip was sufficient. A beep sound would be heard when the measurement is over. The measurement was done three times to determine the average value.
All the data acquired from anamnesis and physical examination were documented on the case report form. Collected data were inputted into the Microsoft Excel 2016 and SPSS® Statistics 20 software (IBM, United States). Data distribution was determined using data normality test. In a normal distribution, average value and standard deviation were used. In abnormal distribution, median value and minimum–maximum value were used.
Unpaired t-test was used to determine to correlation between two normally distributed data, while for two abnormally distributed data, Mann–Whitney nonparametric test was instead used to determine their correlation. Data significance between measurements in the same sample was analyzed using the Friedman test. Significance value in this study was determined using P < 0.05 value.
RESULTS
Sociodemographic characteristic
The sociodemographic characteristics of subjects are presented in Table 1. The range of age in Group A was 18 to 45-year-old with an average of 31.03 ± 8.17 years, while the range of age in Group B was 19 to 42-year-old with an average of 29.53 ± 6.55 years. In Group A, the proportion of subjects who wore hijab for 5–10 years and more than 10 years were equal, however in Group B, the proportion of subjects who wore hijab for 5–10 years is slightly higher than those who wore it for more than 10 years. In both groups, the majority of subjects used hijab made of cotton and wore hijab for 8–11 h every day. Sixty percent of subjects in Group A, and 56.7% of subjects in Group B, wear hijab undergarment regularly. A small percentage of subjects in Group A (6.7%) and Group B (10%) did not use hijab undergarment regularly, while the rest of it never use it. No significant variance in average age or the proportion of length of wearing hijab, duration of wearing hijab, hijab material, and use of hijab undergarment were observed between Group A and Group B.
Table 1.
Sociodemographic characteristic distribution of subjects
| Subjects characteristic | Group A: Frequent hair wash (N=30), n (%) | Group B: Infrequent hair wash (N=30), n (%) | P |
|---|---|---|---|
| Age (years), average±SD | 31.03±8.17+ | 29.53±6.55+ | 0.436a |
| Length (years) of wearing hijab | |||
| 5-10 | 15 (50) | 16 (53.3) | 1.00b |
| >10 | 15 (50) | 14 (46.7) | |
| Duration of wearing hijab every day (h) | |||
| 8-11 | 24 (80) | 22 (73.3) | 0.76b |
| >11 | 6 (20) | 8 (26.7) | |
| Hijab material | |||
| Cotton | 23 (76.7) | 25 (83.3) | 0.747b |
| Not cotton | 7 (23.3) | 5 (16.7) | |
| Use of hijab undergarment | |||
| Yes (always) | 18 (60) | 17 (56.7) | 0.892b |
| No | 10 (33.3) | 10 (33.3) | |
| Sometimes | 2 (6.7) | 3 (10) |
+Average±SD; aUnpaired t-test; bChi-square test. N - Total subjects; n - Number of subjects; SD - Standard deviation
Clinical characteristic
Table 2 describes the clinical characteristic distribution of subjects. The clinical characteristic comprises subjective symptoms documented from anamnesis on the first visit. Nearly, all of subjects in both groups presented with subjective symptoms, which were hair loss, greasy hair, dandruff, or itchy scalp. Seventy percent of subjects in Group A and 86.7% of subjects in Group B complained of hair loss, while greasy hair was experienced by 10% of subjects in Group A and 6.7% of subjects in Group B. Moreover, 36.7% of subjects in Group A and 46.7% of subjects in Group B complained of dandruff. Only a small percentage of subjects in Group A (16.7%) and Group B (13.3%) complained of itchy scalp.
Table 2.
Clinical characteristic distribution of subjects
| Clinical characteristic | Group A: Frequent hair wash (N=30), n (%) | Group B: Infrequent hair wash (N=30), n (%) | P |
|---|---|---|---|
| Subjective symptoms | |||
| Present | 27 (90) | 29 (96.7) | |
| Absent | 3 (10) | 1 (3.3) | |
| Symptoms began/worsen after wearing hijab | |||
| Yes | 21 (70) | 21 (70) | |
| No | 9 (30) | 9 (30) | |
| Hair loss | |||
| Yes | 21 (70) | 26 (86.7) | 0.21a |
| No | 9 (30) | 4 (13.3) | |
| Greasy hair | |||
| Yes | 3 (10) | 2 (6.7) | 1.00b |
| No | 27 (90) | 28 (93.3) | |
| Dandruff | |||
| Yes | 11 (36.7) | 14 (46.7) | 0.6a |
| No | 19 (63.3) | 16 (53.3) | |
| Itchy scalp | |||
| Yes | 5 (16.7) | 4 (13.3) | 1.00b |
| No | 25 (83.3) | 26 (86.7) |
aChi-square test; bFisher test. N - Total subjects; n - Number of subjects
Measurement of transepidermal water loss
Measurements of scalp TEWL of Group A and Group B on baseline, day-14, and day-28 are presented in Table 3. The normality test of TEWL score data on baseline, day-14, and day-28 showed that the distribution was abnormal, so the data were shown in median (minimum–maximum) and were analyzed using Mann–Whitney nonparametric test. There was no significant variance between the median TEWL score of Group A and Group B on baseline. On day-14 and day-28, significant variance was observed (P < 0.05) between the median TEWL score of Group A and Group B.
Table 3.
Scalp transepidermal water loss score on baseline, day-14, and day-28
| Baseline | Day-14 | Day-28 | ||||
|---|---|---|---|---|---|---|
|
|
|
|
||||
| Median | P | Median | P | Median | P | |
| Group A (n=30) | 14.53 (6.9-22.9)+ | 0.668a | 20.07 (12.03-33.13)+ | 0.017a | 20.87 (12.26-50.67)+ | 0.003a |
| Group B (n=30) | 13.65 (8.07-36.3)+ | 17.05 (6.67-37.87)+ | 17.67 (6.43-31.67)+ | |||
+Median (minimum-maximum); aMann-Whitney nonparametric test
Difference of TEWL score between visits was also measured. The measurements of TEWL score difference between day-14 and baseline (D14-baseline), day-28 and baseline (D28-baseline), and day-28 and day-14 (D28-D14) are described in Table 4. The difference of TEWL score on D14-baseline is presented in average (standard deviation) since its distribution is normal, and was analyzed using unpaired t-test. On D14-baseline and D28-baseline, significant variance between the average/median TEWL score difference on Group A and Group B were observed. On D28-D14, there was no significant variance between the median TEWL score difference on Group A and Group B.
Table 4.
Difference of scalp transepidermal water loss score between day-14 and baseline, day-28 and baseline, and day-28 and day-14
| Day 14-baseline | Day 28-baseline | Day 28-day 14 | ||||
|---|---|---|---|---|---|---|
|
|
|
|
||||
| Average | P | Median | P | Median | P | |
| Group A (n=30) | 6.04±5.7+ | 0.008a | 6.45 (−3.07-32.94)++ | 0.005b | 0.17 (−7.33-17.54)++ | 0.929b |
| Group B (n=30) | 1.35±7.4+ | 2.6 (−21.1-16.37)++ | 0.09 (−27.34-11.84)++ | |||
+Average±SD; ++Median (minimum-maximum); aUnpaired t-test; bMann-Whitney nonparametric test. SD - Standard deviation
Measurement of skin hydration
Skin hydration in this study is represented by skin capacitance. Measurements of scalp capacitance score of Group A and Group B on baseline, day-14, and day-28 are presented in Table 5. The normality test showed that the data distribution of skin capacitance score on baseline, day-14, and day-28 was abnormal; therefore, they were presented in median (minimum-maximum) and were analyzed using Mann–Whitney nonparametric test. On baseline, day-14, and day-28, there was no significant variance between median scalp capacitance score of Group A and Group B (P > 0.05).
Table 5.
Scalp capacitance on baseline, day-14, and day-28
| Baseline | Day-14 | Day-28 | ||||
|---|---|---|---|---|---|---|
|
|
|
|
||||
| Median | P | Median | P | Median | P | |
| Group A (n=30) | 13.44 (4.7-34.93)+ | 0.46a | 8.18 (2.57-39.47)+ | 0.359a | 11.48 (4.8-49.87)+ | 0.90a |
| Group B (n=30) | 11.09 (2.0-50.33)+ | 12.52 (4.93-32.17)+ | 12.77 (4.63-32.0)+ | |||
+Median (minimum-maximum); aMann-Whitney nonparametric test
Difference of scalp capacitance score between visits was also measured. The measurements of scalp capacitance score difference on D14-baseline, D28-baseline, and D28-D14 are described in Table 6. Difference of scalp capacitance score on D14-baseline is presented in average (standard deviation) since its distribution is normal, and was analyzed using unpaired t-test. No significant variance between the median scalp capacitance score difference of Group A and Group B were observed on D14-baseline, D28-baseline, and D28-D14.
Table 6.
Difference of scalp capacitance score between day-14 and baseline, day-28 and baseline, and day-28 and day-14
| Day 14-baseline | Day 28-baseline | Day 28-day 14 | ||||
|---|---|---|---|---|---|---|
|
|
|
|
||||
| Average | P | Median | P | Median | P | |
| Group A (n=30) | −1.90±9.02+ | 0.315a | −0.49 (−17.6-41.94)++ | 0.595b | 0.59 (−27.27-38.1)++ | 0.204b |
| Group B (n=30) | −0.34±11.6+ | 0.92 (−28.74-20.27)++ | −0.19 (−18.37-13.4)++ | |||
+Averag±SD; ++Median (minimum-maximum); aUnpaired t-test; bMann-Whitney nonparametric test. SD - Standard deviation
DISCUSSION
The purpose of this study is to establish the influence of different hair wash frequency toward the skin barrier function in women wearing hijab. Hair wash frequency in this study is classified into two categories, frequent hair wash (Group A) and infrequent hair wash (Group B). Frequent hair wash is defined as shampooing once every 1–2 days, while infrequent hair wash is defined as shampooing once every 3–5 days. Those terms were chosen according to the general assumption in Indonesia that the proper hair wash frequency is at least once every 3 days.[9] Furthermore, hair wash frequency is described as a range to avoid inconvenience and increase compliance of subjects.
Sociodemographic characteristic
No significant variance was shown between the average age of Group A (31.03 ± 8.17 years) and Group B (29.53 ± 6.55 years). This study did not include elderly and women in menopause to avoid bias. In general, aging does not influence skin hydration or the ability to prevent water evaporation, however, there is variety of influence according to anatomical location.[13] Hypoestrogenic condition in menopause may also alter collagen content, glycosaminoglycans concentration, and skin vascularization, which might influence skin barrier function.[14]
In both Group A and Group B, the proportion of subjects wearing hijab for 5–10 years and more than 10 years is similar, while the most applied duration of wearing hijab is 8–11 h every day. This study only included women wearing hijab for at least 5 years with the duration of minimum 8 h every day to minimize bias caused by brief period and inconsistent wear of hijab. Other studies that investigated the length of wearing hijab in medical students in Jakarta did not find a significant correlation between prolonged hijab wearing and hair loss.[4] The length and duration of wearing hijab also did not have a significant correlation with the incidence of seborrheic dermatitis in medical students in Semarang.[15] Long duration of wearing hijab (more than 12 h/day) correlates significantly with dandruff incidence according to a study in Bogor in 2017.[16] Until recently, the authors have not yet discovered any studies investigating the influence of the length and duration of wearing hijab on skin barrier function.
Most subjects in Group A (76.7%) and Group B (83.3%) used hijab made from cotton. Cotton is one of the most popular hijab materials used in Aceh, besides jersey, chiffon, and cerruti.[17] However, there is no data available regarding the most commonly used hijab material by Indonesian women, nor its influence on the skin barrier function. Hijab undergarment was used by 60% subjects in Group A and 56.7% of subjects in Group B. In a study by Polat et al. in Turkey, prolonged usage of bonnet (more than 10 years) has been proven to affect the incidence of alopecia, which is believed to be caused by excessive traction produced by the bonnet.[18] No objective data have been found regarding the effect of hijab undergarment on the skin barrier function.
Clinical characteristic
Nearly, all subjects complained of subjective symptoms during the first examination before the wash-out period. Only 10% subjects in Group A and 3.3% subjects in Group B who did not exhibit any symptoms. Subjective symptoms mentioned include hair loss, greasy hair, dandruff, and itchy scalp. These findings indicate that subjective symptoms are common problems in women wearing hijab, although this study did not compare between the symptoms in women wearing hijab and those who do not wear hijab. In general, all subjects did not experience any change in symptoms after the wash-out period.
Seventy percent subjects in Group A and 86.7% subjects in Group B (78.3% of all subjects) complained of hair loss. This supports the findings by Fourina in 2020 that showed a significant gap in hair loss between women wearing hijab (83.3%) and not wearing hijab (53.3%). More analysis on the objectivity of these findings should be done, considering that fallen hair is more accumulated and easily noticed in women wearing hijab, leading to higher possibility if being complained.[19] Traction caused by the hijab undergarment used by most subjects may also contribute to the symptom of hair loss.[18]
Greasy hair was only complained by 10% of subjects in Group A and 6.7% of subjects in Group B (8.3% of all subjects), while dandruff was experienced by 36.7% of subjects in Group A and 46.7% subjects in Group B (41.7% of all subjects). Greasy hair is influenced by sebum secretion on the scalp and hair care habits.[1] The use of hijab may increase scalp humidity, and high humidity may increase the risk of dandruff. There are no objective data that showed the correlation between wearing hijab and greasy hair symptoms. However, wearing two-layered hijab has been shown to increase the risk of dandruff.[20] Hijab undergarment used by most subjects might also contribute to the dandruff symptom reported.
Itchy scalp was only complained by 16.7% subjects in Group A and 13.3% subjects in Group B (15% of all subjects). Itch is a ticklish or uncomfortable sensation on the skin that stimulates the urge to scratch. The itchy sensation is initiated by nociceptor activation which is mediated by the central mechanism through the central nervous system, or the peripheral mechanism through various mediators, such as histamine, prostaglandin, and interleukin.[21] It is still unclear whether the severity of itchy scalp in women not wearing hijab is different than in women wearing hijab. Furthermore, symptom of itchy scalp might also be affected by hair care habit and is heavily dependent on each individual perception.
In order to elaborate the correlation between wearing hijab and subjective symptoms, subjects were asked using a questionnaire regarding the onset of symptoms or whether the symptoms became more severe after wearing hijab. Seventy percent subjects in Group A and Group B claimed that their symptoms first appeared or got worse after they start to wear hijab. This indicates that wearing hijab may induce or aggravate the subjective symptoms on its wearer. Collecting data retrospectively through questionnaire are highly susceptible to recall bias, as it is greatly influenced by individual characteristics, the significance of the incidence, social perception, and the period the incident occurred.[22] Therefore, further studies are needed to assess objectively the influence of wearing hijab toward subjective symptoms.
Measurements of scalp transepidermal water loss and hydration
All subjects underwent wash-out period before scalp TEWL and hydration measurements. During this 14-day period, subjects were instructed to wash their hair once every 3 days using a standard shampoo that was given, with the last hair wash at least 3 days before baseline examination. Hair wash method, including the volume of the shampoo as well the duration of scalp massaging, was explained to the subjects. The purpose of this period is to standardize the scalp and hair condition of the subjects during baseline examination.[23]
TEWL score was measured using the Tewameter® TM300 probe. It is an open-chamber device, comprising an open-ended cylindric chamber with two sensors inside. When placed on the skin surface, water vapor diffusing from the skin surface will pass through this chamber into the environment, and then the two sensors will measure the humidity gradient based on the temperature and relative humidity. Besides open-chamber device, measuring TEWL could also be done using closed/unventilated-chamber and condenser-chamber devices. These three types of devices have good correlation between each other; however, the condenser-chamber device exhibited better sensitivity. Nevertheless, open-chamber device does not occlude the skin, thus permitting skin examination that is closer to its normal condition.[24]
Skin hydration can be assessed by measuring skin capacitance or conductance. In this study, skin hydration was assessed by measuring skin capacitance using the Corneometer® CM825. This device utilizes the capacitor function to store electrical charge and the ability of water to enhance the capacity of a capacitor due to its high dielectric constant. Therefore, high water content inside the skin will show high skin capacitance. On the contrary, conductance assesses skin hydration by measuring the skin electrical conductivity that shift according to its water content. Other methods to assess hydration have been developed, including the image microsensing or skin impedance methods. Until recently, skin capacitance is the standard method to assess skin hydration and it has been applied in numerous cosmetic and dermatological studies, while also demonstrate good correlation with other devices.[25]
Correlation between hair wash frequency and scalp transepidermal water loss
During the baseline TEWL measurement, no significant variance observed between the median TEWL score of Group A (14.53 g/m2/h) and the median TEWL score of Group B (13.65 g/m2/h). Until today, there are no studies regarding the normal scalp TEWL score in the Indonesian population, especially in women wearing hijab. In Caucasian women aged 25–35-year-old, the average scalp TEWL score was 13.0 ± 3.1 g/m2/h with a decrease of TEWL score in the elderly group.[26] Several factors may affect TEWL score, including anatomical location, age, race, and skin care products. These factors influence TEWL score by their action toward sebaceous lipid content, sweat glands activity, occlusion, skin temperature, skin thickness, skin microvascularization, and corneocyte condition.[24] The median scalp TEWL score acquired in this study might also be influenced by the prolonged use of hijab which is known to affect TEWL score through the occlusion effect on the scalp.[5,27,28]
Subjects went through the hair wash frequency intervention according to their respective group, and TEWL score was measured again on day-14 and day-28. Based on the statistical analysis of the correlation between hair wash frequency and TEWL score, the median TEWL scores of Group A were significantly higher than the median TEWL scores of Group B on day-14 (P = 0.017) and day-28 (P = 0.003). In addition, the median TEWL score difference between day-14 and day-28 did not vary significantly in both groups. This indicates that more frequent hair wash may increase scalp TEWL score, and this alteration could already be seen after 14 days of treatment without any significant change after 28 days.
Measuring TEWL is an objective method usually implemented to assess skin barrier function. Skin barrier damage leads to TEWL elevation, on the contrary, more intact skin barrier causes decrease of TEWL.[24] A higher TEWL score in Group A subjects indicates more severe damage on skin barrier compared to Group B subjects. Group A washed their hair more frequently than Group B. The detergent sodium lauryl sulfate contained in shampoo has been proven to damage the skin barrier, therefore, more excessive exposure to shampoo containing detergent might explain the higher TEWL score in Group A.[24]
Based on the Friedman analysis on Group B, it is established that washing the hair once every 3–5 days did not affect the median TEWL score significantly after 14 and 28 days. A more infrequent hair wash should supposedly lower the exposure to detergent and decrease TEWL score. However, the median TEWL score obtained did not significantly differ, instead it tends to increase which indicates the involvement of other factors. In generally, subjects in Group B complained of itchy scalp more frequently during the follow-up (43.3%) compared to the first visit (13.3%). Any form of damage, whether chemically or mechanically, may cause TEWL increase.[29] The more severe itchy scalp symptom might induce scalp scratching and leads to skin barrier damage resulting from mechanical trauma, which indirectly influence TEWL score.
Correlation between hair wash frequency and scalp hydration
On the baseline skin capacitance measurement, no significant variance observed between the median skin capacitance score on Group A (13.435 AU) and the median skin capacitance score on Group B (11.085 AU). In Caucasian women aged 25–35-year-old, the average scalp capacitance score was 32.8 ± 19.6 AU without significant score variance in the elderly group.[26] Until today, there are no studies regarding the normal scalp capacitance score in the Indonesian population, especially in women wearing hijab.
Skin capacitance is determined by the water content inside the stratum corneum, therefore any factors that can modify water content inside the skin will alter skin hydration score. One possible explanation for the huge difference between the scalp capacitance score in this study and other studies is the different pressure applied on the Corneomenter® probe while measuring. The producer of the Corneomenter® device has implemented certain method to standardize the probe pressure using spring system. However, in practice, the measurement could be initiated by different levels of spring pressure, leading to high risk of variation in results between examiners.[30]
Similar to TEWL measurement, scalp capacitance was reevaluated on day-14 and day-28 after subjects went through hair wash frequency intervention according to their respective group. Based on the statistical analysis of the correlation between hair wash frequency and skin capacitance score, there is no significant variances between the median scalp capacitance score in Group A and Group B, either on day-14 or day-28. Until today, there are no studies investigating the correlation between hair wash frequency and scalp hydration. A cohort study in 2008 investigated the correlation between skin washing method with skin barrier damage, and no significant variance was observed on skin hydration after washing by various methods, either using soap or not.[31] Although not comparing washing frequency, that study showed that skin hydration was not influenced by exposure to soap, which indirectly support the result of our study. There is a tendency for the scalp capacitance score to decrease in Group A and to increase in Group B. If followed up for a longer period, there is a possibility that the effect of different hair wash frequency toward the skin capacitance score will be more significant.
CONCLUSIONS
It can be concluded that there is a correlation between hair wash frequency and scalp TEWL in women wearing hijab. However, there is no correlation between hair wash frequency and scalp hydration in women wearing hijab.
Suggestions
Basic data on the normal scalp TEWL and hydration score in women wearing hijab and not wearing hijab in Indonesia should be obtained. Further detailed study which investigates the influence of different hair wash frequencies (i.e., once every day, every 2 days, every 3 days, every 4 days, and every 5 days) toward scalp barrier function in the Indonesian population is also needed. In addition, further studies on factors affecting scalp barrier function, such as different hair wash methods, type of shampoo, or hair length differences, might be useful.
Conflicts of interest
There are no conflicts of interest.
Acknowledgments
The authors would like to express their appreciation and gratitude to all researchers participating in the main study by the Department of Dermatology and Venereology FMUI-RSCM, Dr. Lili Legiawati, SpKK (K), Dr. Sondang P. Sirait, SpKK (K), Dr. Eliza Miranda, SpKK (K), Dr. Windy Keumala Budianti, SpKK (K), Dr. Rahadi Rihatmadja, SpKK (K), Dr. Lis Surachmiati Suseno, SpKK (K), Dr. Peppy Fourina, and Dr. Caroline Oktarina for their guidance, encouragement, and assistance for designing this study and collecting the data. My gratitude is also extended to Prof. Dr. Arini Setiawati, Ph.D. for her help during the statistical analysis of this study.
Funding Statement
Nil.
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