Introduction

Despite its robustness, the skin is susceptible to various disorders, among which acne is one of the most prevalent and psychologically distressing conditions. Acne affects approximately 9.4% of the global population, making it the eighth most common disease worldwide. The pathophysiology of acne is complex and multifactorial, involving increased sebum production, follicular hyperkeratinisation, microbial colonization of the hair follicles by Cutibacterium acnes (formerly Propionibacterium acnes), and inflammation. The formation of comedones, papules, pustules, nodules and cysts is the result of an obstruction and inflammation of the pilo-sebaceous unit.

Skin imperfections cover a wide range of visible skin alterations with a variety of causes depending on age, skin type, ethnicity and associated disorders, lifestyle, stress, hormonal balance, heredity or exposome. The list is long and includes acne, blackheads or comedons, scars caused by these acne phenomena, pore size, hyperpigmentation, senescence stains, white spots, dartres, eczema, rosacea…

These imperfections depending on their severity can have a significant impact on the well-being of men and women, altering their image and interfering in the relationship with others.

Innovative breakthroughs in microbiology, such as microbiome transfers, probiotics or bacteriophages, are being explored to treat acne, mainly through topical application. Nevertheless, an individualized approach that considers psychological aspects remains essential, highlighting the importance of comprehensive care for the affected person.

Not so easy to classify all claims related to skin imperfections

These claims can use the term “anti” or terms related to restoration, improvement. We can distinguish between different categories of claims that can be studied clinically and causally related to different skin signs:

1. Acne-prone skin

• Related to skin pores: Anti-Bacterial, Anti-Black spots, Unclog pores, Comedolytic, Keratolytic, Non-Comedogenic
• Seborrheic status: Anti-Seborrheic, Mattifying, Purifying, rebalancing, Seboregulation
• Inflammatory acne: Anti-Inflammatory, Soothing, Repairing Effect, Healing, Anti-Maskne, Antioxidant, Anti-pollution, respect the barrier function…
• Respect the skin pH

Pollution plays a significant role in inflammatory acne by exposing the skin to harmful particles and toxins. These pollutants can clog pores, increase sebum production, and trigger inflammatory responses, leading to the formation of acne lesions. Prolonged exposure can worsen acne severity and make skin more prone to breakouts.

2. Hyperpigmentation and colour changes

• Hyperpigmentation, such as melasma: Anti-stains,
• Redness: Anti-Rosacea, Anti-Redness, covering effect

3. Surface irregularities

• Relief & topography issues: roughness, uneven skin surface: Anti-drying, smoothing, keratolytic
• Scarring: exfoliating, help the wound healing process, regenerating
• Skin Hydration: moisturizing
• Barrier function

How to evaluate in vivo acne-prone and blemishes skin

The development of acne-prone skin products involves a meticulous process of preclinical and clinical testing to establish their safety, efficacy, and mechanism of action. In the absence of a legislative demand for clinical proof—proof that is required for the claims of sun protection, for instance -the skin care industry often neglects to search for a real treatment.

The field of claims of these complex products is often mixed with those of products intended for sensitive skin, dark skin, young skin… and very often require a multi-criterion evaluation to demonstrate these eclectic performances. Sometimes it seems that the results demonstrated by the before-after photos are the must-have. However, these illustrated results are often consolidated by quantitative measures, dermatological assessments and self-evaluation by the subjects that allow for a comprehensive approach to product activity. The feeling and self-esteem, strongly concerned in the well-being provided by an effective anti-imperfection care routine, will also be able to be further evidence well understood by the consumer.

On the Skinobs Clinical Testing Platform, you can find different claims regarding acne-prone skin and blemishes: anti-black heads, anti-blemishes, anti-seborrheic, astringent, seboregulator… You can find in total 95 methods and 127 providers from 34 countries. Just connect for free, skinobs.com.

On the Preclinical Testing Platform, you can find in total 98 assays and 55 providers in 14 countries, for claims related to acne, sebum, and skin imperfections.

Among the scores by experts’ protocol, the auto-evaluation by the subjects and the neurosensory studies, here are the methods to evaluate these claims.

1. Sebum and lipids quantification

• Image analysis method: Sebufix and sebumeter (Courage+Khazaka), DermaLab Sebum (Cortex), Quantiseb (Monaderm).
• Gravimetric measurement method: SebumScale

2. Skin surface evaluation and image acquisition and analysis: C-Cube Clinical Research, DermaTOP-HE-S, evaSurf, Aeva-HE (Eotech), SpectraCam, NomadCam and SkinCam (newtone), Antera 3D (Miravex), VEOS (Canfield), Clarity (BTBP), Siascope, Visioscan (Courage+Khazaka), Dermalab Videoscope (Cortex)… and others dermoscopes.
3. Lipids composition and quantification in the skin

• Optoacoustic analysis: RSOM Explorer C50
• Shotgun mass spectrometry
• Lipbarvis-HPTLC and Lipbarvis-Microscopy [TEM] (Microscopy services Daenhardt)

4. Face: overall analysis: global image of the face with image acquisition and analysis system: ColorFace (Newtone), EvaFACE-S5, HeadScan Dynamics III, HeadScan V05 – R&D (Orion), VISIA-CR, Visioface (Courage+Khazaka).

While evaluating acne-prone skin and imperfection is important, the overall skin health determine the global aspect of the face including the hypo-seborrheic zones (cheek) and the hyper seborrheic ones (nose, forehead, chin).

5. Microbiota quantification

• Lipbarvis GEN-SSCP analysis, RT-qPCR assays.
• Genome sequencing
• Mass spectrometry
• Profiling and metagenomic sequencing: DNA microarray, Rt-qPCR, 16S-rRNA

Personal care and toiletries are now designed to make the skin healthy. The healthy skin care maintains the skin in good state, protects it from the external aggression and helps to regulate the bad influences of the internal stresses. This is a question of aspect and perceived comfort; it generates a globally positive impression of good health.

It’s crucial for investigators to collaborate closely with Contract Research Organizations (CROs) to meticulously design protocols, define inclusion criteria, establish measurement timelines, treatment conditions, and select optimal devices. Investing time in briefing these essential elements is never wasted; it ensures the integrity and reliability of the study outcomes.

The various high-tech biometrological measurements give the opportunity to connect the technology with the new digital use of personalization from the shop to the bathroom. This connection between objectivation and the digital way of choosing and buying may bring the cosmeticians closer to the reality of marketing. Now the imaging of the skin from the centimetre to the nanoscale is more and more crucial. Whether for no-comedolytic, radiance, anti-dryness, or seborrheic, the several techniques look for higher resolution, larger measurement area, non-invasive, no-contact and direct methods. The algorithms and the statistics are the principal future contribution of the success of these new technologies.

The era of connected devices for scientific skin diagnosis or microbiome analysis combined with the personalization treatment sounds great for skin care evaluation. These digital tools enable the development of new products to answer the new request of consumers.

What are the solutions to validate in-vitro the seboregulation and the inflammation mechanisms in the skin.

The anti-seborrhoeic effect of an active ingredient or cosmetic product can be assessed on human cells, reconstructed skin models or ex-vivo. These approaches not only make it possible to measure sebum production, but also to analyse the mechanisms of action of the substances. To complete these tests, the anti-inflammatory effect can be studied.

Cell tests are carried out on sebocyte lines (SZ95) or primary cultures. Once cell viability has been measured (MTT test), lipid production is quantified by gas chromatography-mass spectrometry (GC-MS) or by analysis (Rt-qPCR) of the expression of target genes coding for lipid biosynthesis.

Tests on reconstructed skin models or ex-vivo models of sebaceous glands make it possible to measure the quantity of sebum on the surface of the skin either by direct measurement or by extraction of lipids and quantification by gas chromatography. Immunohistochemical or protein analyses are carried out to quantify markers of lipid biosynthesis in acne-prone skin: Insulin growth factor-1 [IGF1], SREBP-1, diacylglycerol – DGAT acyltransferase, K7 Cytokeratin 7, Keratinocyte growth factor [KGF], Cutibacterium Acnes [ex-Propionibacterium acnes], Squalene MDA (Malondialdehyde) assay. In addition, the morphology of sebaceous glands can be assessed by histology using specific stains (Haematoxylin and Eosin) or by scanning microscopy.

For the associated anti-inflammatory effect, quantification by protein analysis or gene expression of markers such as : Beta defensin 2-4 [BD-2-4], CD1a, CD209 DC-SIGN, CD44, Cytokeratins 17 [K17], Cytokeratins 6 & 16 [K6, K16], Decorin [DCN], Elafin / Skin-derived anti-leukoproteinase [SKALP], Transforming growth factor beta [TGFβ], Tumour necrosis factor alpha [TNFα], Granulocyte macrophage colony stimulating factor [GM-CSF], Filaggrin [FLG], Interferon gamma [IFNγ], Interleukin 22 [IL-22], 31 [IL-31], 6 [IL-6], 8 [IL-8][CXCL8], 1 alpha and 1 beta [IL 1α-1β], 17 and 23 [IL 17-23], 4 and 13 [IL 4-13], Kallikrein 5 – 7 [KLK-5-7], Langerin [CD207], Thymic stromal lymphopoietin [TSLP], Matrix metalloproteinases [MMP], Oncostatin M [OSM], Prostaglandin E2 [PGE2], Cathelicidin antimicrobial protein [CAP18], Ribonuclease 7 [RNASE7], Sirtuin 1 [SIRT1]. In addition, the measurement of Reactive Oxygen Species (ROS) is a good indicator of oxidative stress linked to inflammation.

In conclusion, in-vitro assessment of the anti-seborrheic effect on cells requires a combination of quantification techniques to identify and characterize the active compounds.