Commentary

There are many publications documenting skin changes due to ageing. What is interesting and new about this study is the authors’ focus on the scalp, as age-related changes in scalp skin have received very little attention in scientific researches up to now. When it comes to ageing, mentions to the scalp are usually about hair greying or hair loss. This study attempted to describe functional and structural modifications in scalp skin with ageing, working maybe as a milestone to future researches in this area.

Introduction

Skin changes with ageing. There are many articles in the scientific literature describing this process. Despite variations between skin areas, gender or ethnic origin, aged skin is frequently characterized by a lower transepidermal water loss, a higher capacitance, a slightly lower sebum casual level and a stable temperature. The scalp skin has not been well described and documented, apart from work on specific disorders such as alopecia or dandruff. Similarly, age-related alterations in scalp skin have not yet been studied. This study aimed to address the modifications on the scalp caused by ageing using instrumental and imaging methods. Initially, the authors focused on changes occurring in scalp skin of Caucasian women of two distinct age groups. The small sample of this cohort is one limitation, as it could be unrealistic to extrapolate the conclusions to the overall population.

Methods

The study involved 15 Caucasian female volunteers aged 25–35 years, referred to as younger group, and 15 Caucasian female volunteers aged 60–65 years, referred to as older group. The physiological parameters were evenly measured on a 2 cm² area of the scalp, after cutting the hair at the level of scalp surface. Volunteers were instructed to wash their hair and scalp 48 h before the measurements, using a bland shampoo. Sebum content was recorded using a Sebumeter. Transepidermal water loss was recorded in triplicate using a Vapometer. Capacitance, as an index of stratum corneum hydration, was measured using a Corneometer. The temperature of the scalp surface was recorded using an infrared thermometer.

Imaging of the scalp was carried out a few weeks after the physiological measurements. In addition to scalp area, imaging of the forehead as a close skin site was also performed. Skin thickness and ultrasonic features of the dermis were recorded by the ultrasound system. Images of the scalp were also acquired using an optical coherence tomography system, which is an interferometric, non-invasive tomographic imaging technique adapted to in vivo investigation of the skin. Statistical analysis was then carried out using a specific statistic software. For each parameter, mean and standard deviation (SD) were computed, and the normality distribution and homogeneity of variance were both calculated.

Results

Regarding the physiological parameters, the findings showed that the transepidermal water loss tends to decrease with age. Casual sebum level appears slightly lower in the older group. However, despite a relative decrease of 20%, no significant age effect was found. Capacitance did not vary among age groups. Finally, the temperature of the scalp surface significantly decreases in the older group.

Imaging through the Ultrasound system demonstrated that the skin appeared thicker (Dermis and Epidermis in the older group than in the younger group on both scalp and forehead. Echogenicity of superficial dermis decreased significantly with age on the forehead while keeping stable on the scalp. Echogenicity of deep dermis did not show any change with age on both scalp and forehead. A large variation was observed between the two anatomical areas, with a significantly higher echogenicity of superficial dermis and lower (threefold) echogenicity of deep dermis on scalp, as compared with the forehead. Also, with age, the pseudoattenuation increased significantly on the scalp while it was unaltered on the forehead.

The images captured by the OCT system showed that the corneum thickness was found significantly lower in the older group on the forehead, while it was unchanged with age on scalp. Epidermal thickness on the scalp appeared significantly lower in the older group than in the younger, while stable with age on the forehead. The dermal epidermal junction significantly flattened with age on the forehead. On the scalp, it was found a small decrease in undulation with age, albeit non-significant.

Discussion

Scalp surface temperature decreases a little with age. Although increased dryness in aged skin is generally agreed, no change in capacitance measurements was found in this study. A lower transepidermal water loss is commonly associated with a more efficient skin barrier function. Overall, this decrease is more likely linked to a slowing down of scalp metabolism rather than changes in the various barrier components. The sebaceous function is known to change with age as sebum secretion is well linked to the systemic hormonal status. Despite a slightly lower level in the older group, the casual sebum level on scalp did not show significant change with age. As seen on the forehead, the sebaceous function plateaus are in the 30s, slowly decreasing thereafter, with a more pronounced decline from menopause.

There is no clear consensus in the literature about changes in skin thickness with age according to skin site. Skin thickness is highly influenced by sun exposure. A thinning of inner forearm skin and a thickening of facial skin are commonly agreed. In this study, skin thickening with age was observed at least on the forehead and specifically on the vertex scalp. Both forehead and vertex scalp get thicker with age as they are sun-exposed areas. Echogenicity did not change with age in both superficial and deep dermis of the scalp. On forehead, only echogenicity of superficial dermis seems to have decreased with age, as frequently described in the literature. With age, an increase of the pseudoattenuation on the scalp was observed with still negative values. Such increase is mostly explained by the increase in skin thickness.

In summary, this study confirms that the scalp is functionally and structurally affected by ageing as other areas of the skin. Age-related changes do not only reflect on hair growth and color; evidence shows they also affect interfollicular skin scalp.