Lin Xianting, Yang Jianzhong

Beauty Hi-tech Innovation Co., Ltd., Kobe, Japan

Abstract Scalp in flammation is a fundamental issue to many unhealthy scalp symptoms such as itching, redness,dandruff, and odor. Oxidized sebum, or specifically oxidization of the squalene component in sebum, is one of the key reasons causing scalp in flammation. Therefore, antioxidation of the sebum is an important way to maintain scalp health. In this study, we investigated the relationship between squalene peroxide formed and its exposure time under UVA light. Further, we found two oil-soluble antioxidants, ginger root extract and vitamin E,being effective on antioxidation of sebum, and can be potentially used as scalp care actives.

Key words scalp health; in flammation; sebum oxidization; UVA exposure; oil-soluble antioxidant

Introduction

People can easily image the scalp being like soil where the hairs grow like plants. If the scalp is healthy, the hair will grow well, just like the soil having good quality will allow a harvest. More and more customers focus on scalp healthy rather than hair care alone, and emerging markets for scalp care products are becoming the new trend. A recent study reports that when the scalp has inflammation, the inflammatory factors will affect the ability of hair follicle cells, resulting in decreased hair strength and elasticity.[1]A model of potential technical approaches for scalp care were previously published as a triangle theory including three elements, i.e., reducing irritation, improving scalp defense, and activating hair follicle cells as illustrated in Figure 1.[2]

Figure 1. Technical approaches for scalp care

When the scalp is unhealthy, symptoms such as dandruff,itching, redness, and odor can occur and all of these are related to sebum. It is known that the scalp surface is rich in hair follicles and sebaceous glands. The sebaceous glands secrete 1～ 2 g of sebum every day. The fresh sebum functions as the scalp barrier and keeping the scalp moisturized. On the other hand, sebum can easily absorb dust, which is the main cleansing target of hair shampoo. Also, there is a strong connection between scalp inflammation and aged sebum.For example, it is known that triglycerides in human sebum can be broken down by Malassezia fungi into saturated and unsaturated fatty acids. Saturates are consumed by Malassezia, and the abundant the unsaturates left on the scalp can penetrate and induce inflammation.[3-5]Therefore, using Malassezia inhibitors has been the key technical approach for anti-dandruff shampoos over the past decades. More importantly, the squalene in sebum remaining on the scalp can be oxidized by ultraviolet rays or air pollution such as PM2.5, resulting in irritative lipid peroxides. It is reported that the oxidized squalene is remarkedly increased and the squalene is decreased at sites of inflammatory scalp region,[6]indicating that the squalene peroxide is one of the key potential factors causing scalp inflammation.

In this paper, we conductedin-vitrostudies on oxidation and antioxidation of squalene, and the effects on scalp inflammation.

Result and discussion

Sebum oxidation by UV and its effect on in flammation

Figure 2. Effect of UVA exposure on oxidation of sebum

The experiments herein included squalene oxidation study and inflammation factor measurement. The squalene oxidation procedure is as follows: expose the squalene sample under UVA for 5 to 24 hours; followed by measure the peroxide value (POV). The inflammation factor measurement procedure is as follows: treat the HacaT cells for 24 hours with 0.01% lipid obtained from the above study; use RNeasy mini kit to collect RNA; prepare cDNA via reverse transcription reaction by using High Capacity cDNA Reverse Transcription Kits; quantify the IL-1 alpha mRNA via real-time PCR by using FastStart Essential DNA Green Master.

As observable in Figure 2, the POV of squalene after UVA exposure was significantly increased, indicating that the squalene was oxidized by UVA and the POV increased with increasing the time of UVA exposure. As shown in Figure 3,oxidized squalene after UVA exposure induced an increase of inflammatory cytokine IL-1 alpha. Therefore, it is concludable that squalene in sebum can be easily oxidized by UVA, and the oxidized squalene peroxide can indeed cause inflammation.

Antioxidation of sebum

Now our objective has been shifted to antioxidation of sebum or specifically the squalene in the sebum. The usefulness of Vitamin E as an antioxidant in skin care products has been well researched. Therefore, it would be interesting to investigate if Vitamin E can also act as an antioxidant for sebum. In addition, ginger root extract is one of the most popular plant-based actives in China, having potential as an antioxidant as well. However, the traditional ginger root extracts are water-soluble and unable to interact with the oily sebum. Fortunately, we found an oil-soluble extract of ginger root that was sourced from Tahiti and extracted with supercritical carbon dioxide.

The experiments herein included squalene antioxidation study and inflammation factor measurement as well. The squalene antioxidation procedure is as follows: mix 1% testing ingredient with squalene; expose the mixture under UVA for 5 hours; measure the peroxide value (POV). The inflammation factor inhibition test steps referred to section “Sebum oxidation by UV and its effect on inflammation”. The testing samples were from the squalene antioxidation study as described above.

Figure 3. Evaluation of in flammation by Real Time PCR for IL-1 alpha

Figure 4. Evaluation of Anti-oxidation on sebum

Figure 5. Evaluation of in flammation by Real Time PCR for IL-1 alpha

As observable in Figure 4, Vitamin E and ginger root extract both showed significant antioxidation effect when premixed with the squalene. More specifically, POV of the squalene sample treated with ginger roots extract was lower than that of treated with Vitamin E, and was equal to the squalene without any UVA exposure, indicating its perfect effect on antioxidation of sebum. The results in Figure 5 showed that inflammation response was suppressed when the squalene was pretreated with Vitamin E or ginger root extract.

Conclusion

Through this study, it can be concluded that the squalene peroxide will irritate the scalp to trigger inflammation and potentially causing scalp itching, redness, dandruff, and odor. It is experimentally proven that the induced scalp inflammation is proportional to the resulted amount of sebum peroxide. In order to prevent scalp inflammation, this study proved antioxidants including the well-known vitamin E as well as the selected oil-soluble ginger root extract are both effective on antioxidation of sebum and hence preventing inflammation of scalp, while ginger root extract showed higher effect than Vitamin E.

The antioxidation of sebum will reduce the chance of irritation of scalp and prevent the inflammation caused by sebum peroxide, which is an important step of the triangle theory for scalp care (Figure 1), opening a new direction for scalp care technology development. While two effective sebum antioxidants have been identified through this study, more of such ingredients and their applications in scalp care products will be an important topic for future technological innovation of scalp care.