Influencing Factors and Solutions of Oily Sensitive Skin

Yang Suping,Zhao Wenxuan

Beijing Bloomage Hyingc and Technology Co.Ltd.,China

Abstract The influence factors of oily sensitive skin were reviewed.Some solutions were proposed for the devel opment of skin care formulations that aim at solving the oily sensitive skin problems more effectively,such as repairing the skin permeability barrier,controlling oil,inhibiting sebum oxidation,relieving keratinization abno rmalities,regulating the skin microecology and alleviating skin inflammatory reactions.It was concluded that f uture research should focus on precise skin care by designing targeted product formulations according to the ch aracteristics of oily sensitive skin.

Key words oily sensitive skin;acne;cosmetics

Due to the increase in demand for precision skincare,more and more consumers are seeking skincare products specific for their own skin types.Leslie Baumann proposed the Baumann Skin Type Indicator (BSTI) to classify skin types.Four dichotomous parameters are used to characterize facial skin types: dry or oily,sensitive or resistant,pigmented or nonpigmented,and wrinkled or unwrinkled.The Oily sensitive (OS) skin is characterized by both oiliness and sensitivity[1].The sebaceous glands in the T-zone of OS skin are relatively strong,making it prone to acne vulgaris,rosacea,seborrheic dermatitis and other skin problems[2].On the other hand,the cheek area is dry and sensitive,easily affected by various internal and external factors leading to uncomfortable feelings,such as itching,burning,stinging,dryness or tightness.In addition,erythema,desquamation,and other symptoms may occur[3].Compared with dry sensitive skin,the treatment of oily sensitive skin is more complicated.This article focuses on theinfluencing factors and solutions of OS skin.

1 Influencing factors

1.1 Epidermal permeability barrier

The stratum corneum (SC),as the primary mediator of the epidermal permeability barrier function,plays roles in regulating the moisture and microbial balance,preventing the formation of reactive oxygen species,reducing ultraviolet radiation damage to the skin,and resisting allergic reactions caused by external allergens.The formation of OS skin is closely related to the weakened skin permeability barrier function affected by the amount and proportion of intercellular lipid components.Yamamoto et al[4]analyzed several parameters of acne patients and non-acne patients,and found that theincreased sebum secretion and Trans Epidermal Water Loss (TEWL) and the decreased levels of ceramides and free sphingosine led to the defects of the bilayer lipid membrane between keratinocytes and resultedin the reduced permeability barrier function.

The epidermal permeability barrier functionis also affected by the SC pH value.This may be because several key enzymes in the synthesis of lipid components are pH-dependent.For example,acidic phospholipase and beta-glucocerosinolipase,which affect ceramide synthesis,require pH values of 4.5 and 5.6 respectively.When the pH value rises to neutral,the activity of the enzymes will decrease significantly[5].In addition,the antibacterial components and nitrites in sweat have the best bactericidal activity when pH value is 5.5[6].As the pH increases,the resident flora changes,making the epithelium susceptible to infection,resulting in permeability barrier dysfunction.Chaitra Prakash et al.compared the pH of five areas of the face of 200 people with normal skin and 200 people with acne in Africa,and found that the average facial pH of of normal skin was 5.09 ±0.39,and the average facial pH of acne patients was 6.35 ± 1.30.There is no significant difference between the average facial pH of men and that of women[7].From the results,we find that the facial pH value of acne patientsis significantly higher than that of normal skin.The increase of pH affects the permeability barrier function to some extent.

1.2 Excessive secretion of sebum and lipid peroxidation

Sebum is a kind of lipid mixture secreted by sebaceous gland cells.The adult sebum is composed of triglyceride and free fatty acids (57.5%),wax esters (26.0%),squalene (12.0%),Cholesteryl ester(3.0%) and cholesterol (1.5%)[8].Sebum can lubricate the skin and inhibit the invasion of pathogenic microorganisms.In addition,recent studies have shown that sebum can also deliver the lipid-soluble antioxidants to the surface of the skin,such as coenzyme Q10,vitamin E and squalene.Squalene acts as a candidate antioxidant when the coenzyme Q10 or vitamin E is deficient[9].

The average sebum production in healthy adults is around 1.0 mg/10 cm2every 3 h.And itis considered excessive if the sebum production exceeds 1.5 mg/10 cm2every 3 h[10].Excessive sebum secretion not only make the skin overly oily and enlarged pores that affect the skin beauty,but also result in a series of skin problems.Donald et al speculated that increased sebum secretion would dilute linoleic acid in sebum,and led the hair follicle epithelial cells to essential fatty acid deficiency state,which induced the hyperkeratosis and barrier dysfunction[11].The increased sebum secretion and the altered lipid composition and the ratio of oxidants and antioxidants are the main factors associated with acne.Mainly due to the squalene peroxidation and reduced levels of vitamin E,the lipids in the sebum are peroxidated.The lipid peroxides can induce keratinocyte to proliferate and differentiate,andinduce the production of Proinflammatory Cytokine and the activation of the Peroxisome Proliferator-Activated Receptor (PPAR)[12].

1.3 Skin dysbiosis

The skin microbiota is composed of bacteria,fungi,viruses,mites and other microorganisms colonized on the skin surface and glands[13].The skin microbiota interacts with the host skin and immune system through proliferation and secretion,forming the skin microecosystem[14].According to colonization time,the flora on skin surface was divided into resident flora and transient flora.The resident flora include Cutibacterium acnes (C.acnes),Staphylococcus epidermidis(S.idermidis) and Malassezia,etc.The transient flora include Staphylococcus aureus (S.aureus),streptococcusCandid,a albicans,etc.Transient flora is the main factor causing skin infections[13].Antimicrobial peptides produced by resident flora can inhibit and kill pathogenic bacteria.The total number and composition of skin microbiota are associated with the skin surface pH,fatty acid composition and humidity[15].Due to excessive sebum secretion,oily sensitive skin is more conducive to the growth of lipophilic microorganisms,such as C.acnes,corynebacterium and fungus Malassezia.And this results in bacterial flora disorder.Bacteria that are beneficial to their hosts can become pathogenic in some cases.For example,C.acnes can release various enzymes affecting skin health,such as hyaluronidase,protease,phosphatase,neuraminidase and CAMP (Christie-Atkins-Munch-Peterson) factors.Hyaluronidase degrades the hyaluronic acid of connective tissue.While other enzymes damage the integrity of epidermic cells,and then damage the integrity of hair follicle wall and cause inflammation[16].Malassezia hydrolyzes sebum through lipase and phosphatase,resulting in triglyceride reduction and free fatty acids increase,leading to seborrheic dermatitis[17].In addition,Malassezia also converts saturated fatty acids into unsaturated fatty acids,increasing skin irritation.

1.4 Inflammatory response

Oily sensitive skin with acne or dermatitis is accompanied by inflammation.The characteristics of inflammatory acne are papules,pustules,nodules and abscesses[18].In inflammatory acne,symptoms such as dull color,erythema and scar can be observed in the skin lesions at the later stage of inflammatory reaction[19]. C.acnes play a key role in the occurrence and development of inflammatory acne and produce free radicals by secreting lipases,chemokines,matrix metalloproteinases and porphyrins,which lead to skin inflammation by damaging keratinocytes.In addition,C.acnes increase the expression of pro-inflammatory cytokines such as interleukin-1β (IL-1β),interleukin-6 (IL-6),interleukin-8 (IL-8) and tumor necrosis factor α(TNF-α) through human keratinocytes,sebaceous cell or macrophages,and trigger the inflammatory response of acne vulgaris[18].Moreover,the synthesis of chemokine or cytokine in human monocytes is induced by Toll-like receptorin the C.acnes-induced dermatitis[20].Toll-like receptors can activate the core signaling pathways,transcription factors,Nuclear Factor kappa-B (NFκB) and Mitogen-Activated Protein Kinase (MAPK)during inflammation[21].As mentioned earlier,the pathogenesis of seborrheic dermatitis is related to the proliferation and metabolism of Malassezia,whose metabolism produces free fatty acids that stimulate keratinocytes to secrete inflammatory factors such as interleukin-4 (IL-4) and interleukin-10 (IL-10).These inflammatory factors increase the expression of fat synthase and lipid metabolism transcription factors to promote lipid synthesis and aggravate seborrheic dermatitis[22].

1.5 Neurogenic inflammation

Oily sensitive skin can be more prone to high nerve and blood vessel response under the stimulation of internal and external factors,which cause itching,burning,tingling,dryness or tightness[3].Epidermal Transient Receptor Potential (TRP) channels play a critical role in this process.Currently,TRP channels consist of 6 subfamilies,a total of 28 kinds of channel proteins,including TRP canonical (TRPC),TRP vanilloid (TRPV),TRP melastain (TRPM),TRP ankyrin(TRPA),TRP polycystin(TRPP) and TRP mucolipin(TRPM) channel subfamily[23].The capsaicin receptor TRPV1 is the most widely studied channel protein in the TRPV family.Its activation caninduce the release of neuropeptides,which are pro-inflammatory mediators,such as neurotransmitter P(SP) and Calcitonin Gene-related Peptide (CGRP).Furthermore,the release of Substance P can cause vascular reactive pruritus,and CGRP can trigger blood vessel dilation.Meanwhile,the above series of reactions lead to neurogenic inflammation[24].In general,TRP channels,as thermoreceptors and chemoreceptors of different groups of peripheral sensory nerve cells,get involved in the occurrence and development of sensory nerve mediated pain,pruritus and neurogenic inflammation,as well as in the occurrence of skin diseases related to sensory nerve mediated mechanisms[25].

1.6 Other

There are many other factors that influence OS skin,such as diet,stress,ultraviolet light,cosmetics,and so on.In terms of diet,there is a strong association between foods with a high Glycaemic Index (GI) with the long-lasting acne,while a low GI diet reduces the risk of acne[26].

Stress is also related to the formation of OS skin,Toyoda reported that skin nerve factor such as neuropeptides,neuropeptide degrading enzymes and neurotrophic factors induced the increase of sebaceous gland volume and lipid synthesis through substance P,thus inducing C.acnes infection and possibly increasing inflammation mediated by sebaceous mast cells[27].In addition,interindividual differences that may play a role in sensitive skin formation include skin barrier permeability,dose and number of chemical exposures to allergens,regulatory T cell activity,and interindividual differences in T cell repertoires.Prior studies show that there isinterindividual variability in the frequency of CD1arestricted T cells in the blood and skin of healthyindividuals an differences in CD1a-autoreactive response rates in skin[28].

2 Solution

2.1 Reparation of the skin permeability barrier

The skincare products can be developed to repair the skin permeability barrier by the following aspects.

Suitable humectant should be selected to hydrate the skin and decrease TEWL.Csilla and others[29]revealed that the glycerol-and xylitol-containing gel could significantly increase the water content in the superficial and deeper layers of the skin and improve barrier function of the skin over a short period.Humectant commonly used in cosmetics include sodium hyaluronic acid,glycerin,trehalose,and betaine.

Physiological lipid mixtures should be supplemented with the appropriate proportion[30].The restoration of the disrupted permeability barrier function can be accelerated when the proper molar ratio of cholesterol,ceramides,and fatty acids are applied[31-33].However,the barrier repair will be delayed if only one or two of the three lipids are applied.Tan Yimei and others compared the effects of physiological lipids with different ratios on barrier repair.They discovered that the short-term use of a physiological lipid mixture dominated by ceramide (ceramide : cholesterol : free fatty acid=3:1:1) had a better repair effect than lipid mixtures with equal molar ratios and lipid mixture dominated by cholesterol and free fatty acid[32].In addition to supplementing physiological lipids,some raw materials are used to promote the internal synthesis of lipid components,such as rambutan peel extract that can promote epidermal ceramide synthesis[34].

The pH of resident skincare products should be controlled within the faintly acid range so that the lipid synthesis enzymes associated with barrier function can be in its best active state.After using alkaline cleaning products,faintly acid products are recommended to apply to restore the faintly acid condition of the skin.

2.2 Oil control and inhibition of sebum oxidation

There are two methods used to control oil : (i)reducing sebum-secreting by inhibiting the sebaceous glands function;(ⅱ) the physical adsorption of oil thatimmediately improves the condition of oily light on the face surface.Generally,two methods are used in combination to achieve short-and long-term oil control.

Due to the sebaceous gland function is related with the activity of 5α-reductase,particularly Type I 5α-reductase[35].Some ingredients that can inhibit the activity of 5α-reductase are applied in the formulation to achieve the purpose of oil control.For example,zinc PCA,hydrolyzed zinc hyaluronate,bioflavonoids,rhizoma smilacis glabrae,and so on.In addition,the sebum-secreting is influenced by the sebaceous cell proliferation and the number of active sebaceous glands.The relative efficacy ingredients include mango leaf extract and 10-hydroxydecanoic acid.

The raw materials that control oil by physical adsorption include silica,amylopectin,and polymer powder.These raw materials can be used onlyin opaque products.In addition,a extracellular polysaccharide with hydrophobic amino acid structure has been developed to absorb sebum intoits network to achieve an immediate oil-controlling effect.This raw material can be used in transparent water-based formulations.

The raw materials commonly used forinhibition of sebum oxidation include fullerene,epigallocatechin gallate,ascorbgyl palmitate,vitamin E and its derivatives and anthocyanins.

2.3 Treatment of keratinization abnormalities

Fruit acids and β-hydroxy acids are often used in cosmetics to treat oily skin keratosis[36].The principleis that these acidic materials can weaken or loosen the connections between keratinocytes[37].In addition,the acidic environment can inhibit the proliferation of propionibacterium acnes.Thus acnes can be controlled and post-inflammatory hyperpigmentation can be improved[38].

The raw materials in cosmetics for correcting abnormal keratinization include salicylic acid and first-to third-generation fruit acids.Salicylic acidis a type of β-hydroxy acids.As a lipophilic acid,it can penetrate deep into pores to improve keratin abnormalities.In recent years,salicylic acid composite materials that modified by cyclodextrin or acacia senegal have been developed to achieve the effect of slow release of salicylic acid and reduce stimulation.Recently,consumers prefer salicylic acid derived from plants,such as white willow bark extract.

The three generations of fruit acids have different characteristics.Due to the small molecular weight,the first generation of fruit acids,such as glycolic acid and lactic acid,rapidly penetrate the stratum corneum,which may cause skin irritation,redness and swelling.The second generation of fruit acids usually refers to glucose lactone,which is hydrolyzedinto gluconic acid when exposed to water.This polyhydroxy acid is milder than the first-generation fruit acid.Aldonic acid is the third generation of fruit acids,formed by combining a sugar molecule with gluconic acids,such as lactobionic acid and maltose acid.Compared to the first-and second-generation fruit acids,these fruit acids are milder and have a better moisturizing effect,suitable for the skin withimpaired barrier function.

2.4 Regulation of the skin microbiota

Regulation of the skin microbiota is to regulate the interaction between microorganisms and hosts,and aims at restoring the balance of flora andimmunity[39].Common regulation methods include oral probiotics,drug treatment,and microbiota transplantation.In cosmetics,the raw materials that regulate the micro-ecology of the skin are mainly divided into three categories based on their source and mechanism of action: prebiotics,probiotics,and postbiotics[13].Prebiotics are primarily carbohydratebased foods for beneficial bacteria,such as sorbitol,xylitol.Probiotics are microorganisms that are active and beneficial to the host’s health.However,it’s infeasible to add probiotics in cosmetics for the preservatives and regulations in China Postbiotics are the probiotics' metabolites or lysates which have direct or indirect effects on the host.Typical raw materials include yeast lysate,lactobacillus ferment lysate,and vitreoscilla filiformis lysis solution[40].

2.5 Relief of skin inflammatory reactions

Typically,skincare products for sensitive skin are developed with soothing effects by reducing the expression of inflammatory factors and alleviating theinflammatory reaction.In addition,pain and itching feelings can be alleviated by acting on the sensory nerve receptors[41].

The raw materials that applied in cosmetics for soothing effects act in the following aspects: (i)Reducing the inflammatory reaction by inhibiting the release of inflammatory factors,such as PGE2,TNFα,IL-1β,and NF-κB.The relevant ingredients include acetyl dipeptide-1 cetyl ester,licochalcone A[42,43],asiaticoside[44],and olive leaf extract[45].(ⅱ) Treating swelling by reducing local vascular dilatation.The relevant ingredients include portulaca oleracea extract[46]and dandelion extracts[47].(ⅲ) Reducing the neurological inflammation and the activation of neurons by blocking TRPV1 receptors to relieve the feelings of pain and burning[48].The relevantingredients include pogostemon cablin leaf extract,4-t-butylcyclohexanol,etc.

3 Summary

With the increased awareness of skin care,consumers would be more willing to choose the skin care products suitable for their own skin type.It is possible to develop the targeted products for different skin types based on the dermatological studies.OS skin requires controlling oil secretion and solving oilrelated problems while being gentle.It should also soothe and repair skin barrier function and adjust skin microflora.A safe and effective product can be developed when all aspects mentioned above is takeninto consideration.