Instrumental measurements have been made possible by over 70 years of analytical research and engineering of dermatological tools and have continued to grow in importance in assessing skin characteristics. Tools for measuring hydration, water loss, oiliness (sebum) and skin turnover have been benchmarked since the 1980’s, and thousands of papers utilizing these instruments exist in the literature of skin research. More particularly, the area of skin imaging has exploded in recent years with 2D and 3D image analysis devices and corresponding software being readily available to quantify parameters such as pore size, eye bags, depth of facial wrinkles, scalp hair and cellulite. All the approaches provide “quantitative” results that can then be characterized as percentage variation (e.g., increased moisturization by 20%, reduction of wrinkles by 30%, etc.). This quantitative data is often combined with qualitative data by way of a test subject self-assessment questionnaire, so that the manufacturer can better understand how the product’s perceived versus actual performance benefits are reconciled.

Reliable studies should include several measurements to increase the study’s robustness and the opportunity for secondary analysis. One or two outcomes (primary endpoints) should be chosen to assess the degree of efficacy realized and to provide substantiation of the claimed effect. For example, one way of evaluating the efficacy of a moisturizing claim is to measure water content within the stratum corneum (hydration), whereas the measurement of a product’s effect on skin barrier function is determined by measuring the amount of water evaporating from the surface of the skin (trans-epidermal water loss or TEWL). See, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4969411/ for additional information.

This section explains the primary in-vivo product efficacy evaluation parameters and the instruments used to measure them, in order to substantiate product efficacy. More details on each measurement method can be found in our Instrumentation section.

Skin Hydration/Moisturization Testing
Corneometry is a technology used to measure the hydration of the outer layer of the epidermis (stratum corneum). As the skin is a dielectric medium, variations in hydration show up through changes in capacitance, i.e., the ability of the skin to conduct electricity. In order to evaluate the skin’s moisture content, a measuring capacitor is pressed against the skin using constant pressure and the electrical capacitance readings are then evaluated. The device used to make these measurements is known as a Corneometer®. The reading it generates corresponds to the cutaneous hydration levels both before and after treatment with a cosmetic product, to assess its effect on skin hydration/moisturization. If the degree of capacitance increases (the more water present, the greater the capacitance) after use of a product, this confirms that the product is effective at increasing skin hydration/moisturization. Moreover, the data points can be used to quantify the degree of hydration on a percent basis. See, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4268288/ and https://www.researchgate.net/publication/314923242_Measurement_of_Skin_Surface_Hydration for additional information.

Skin Barrier/Trans-Epidermal Water Loss Testing Trans-epidermal water loss (TEWL) is the most widely used objective measurement for assessing the barrier function of skin in healthy individuals, as well as patients with skin diseases that are associated with skin barrier dysfunction, such as atopic dermatitis. TEWL represents the quantity of water vapor that diffuses across a fixed area of stratum corneum to the skin surface and is lost to the air per unit time. The amount of water evaporating from the skin surface is measured using a probe that is placed in contact with the skin surface and contains sensors that detect changes in water vapor density (i.e., humidity and temperature sensors). TEWL can be measured using an open-chamber, unventilated-chamber, or condenser-chamber device. It is a sensitive measurement that is affected by properties of the surrounding microclimate such as environmental humidity, temperature, and airflow and as a result needs to be measured under controlled conditions. A decrease in TEWL after product usage corresponds to an improvement in barrier function. See, https://pubmed.ncbi.nlm.nih.gov/29923639/ and https://pubmed.ncbi.nlm.nih.gov/30348333/ for additional information.

Skin Restructuring Testing
A device known as a Squame Scan® is used to evaluate the barrier function of the external layer (epidermis/stratum corneum) of the skin. As skin ages, its barrier function capabilities decrease. In order for skin’s stratum corneum to effectively protect the body from external aggressors like sunlight and pollution, as well as retain moisture to prevent it from becoming overly dry, it must exhibit good barrier function. Skin’s barrier function is directly related to the amount of carbonylated protein present within the stratum corneum. When evaluating skin’s barrier function, specially designed tape is applied onto the surface of an individual’s skin and then removed. Upon removal, dead skin cells taken from the stratum corneum are adhered onto the tape strip. The Squame Scan® then measures the protein content in the dead skin cells on the tape, to ascertain the stratum corneum’s barrier function capabilities. A decrease in carbonylated protein content within the stratum corneum following use of a product confirms its ability to restructure the skin and enhance its barrier function capabilities. See, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4730153/ for additional information.

Sebum Control Testing
Excessively oily facial skin is caused by overactive sebaceous glands which can affect both males and females. Those who suffer from this skin type have skin that is greasy, shiny, and with large pores, rendering it more prone to acne and seborrheic dermatitis. If a product is marketed as being useful for aiding those with oily skin, its ability to help inhibit sebum production is evaluated. Sebum production levels on a person’s forehead and cheeks are measured using a photometric device called a Sebumeter. The quantity of sebum present on the mid- forehead is determined using sebum collector tape, that absorbs the serum from the skin area being tested. The more sebum that is absorbed, the more optically transparent the tape becomes. The amount of sebum is quantified by the sebumeter as an absorption measurement of the tape. Measurements are taken prior to treatment and after several weeks of treatment (before and after treatment). A decrease in the amount of sebum present on the surface of the skin evidences the efficacy of the product. See, https://pubmed.ncbi.nlm.nih.gov/26114451/ and https://www.researchgate.net/publication/232430355_EEMCO_Guidance_for_the_in_vivo_Assessment_of_Skin_Greasiness for additional information.

Skin Elasticity and Firmness Testing
As a person ages, both the firmness and elasticity of their skin naturally decrease over time. In assessing the efficacy of an anti-aging product that claims, a Cutometer® is used to simultaneously measure both skin elasticity and firmness. This instrument employs a suction-generating probe, in combination with specialized software, to assess elasticity and firmness. The probe is placed on a small patch of skin and activated to generate a gentle suction causing skin to be drawn into the probe, after which it is released and allowed to recover. The device measures the quantity of skin captured during the suction process based on how deeply and quickly the skin is drawn into the probe. This data point is used to assess skin firmness, it being understood that firmer skin will be more difficult, and take longer, to capture during the suction step. Once the suction step is concluded the skin is released and allowed to recover with measurements being taken during the entire recovery process. The length of time it takes the skin to recover to its original state represents the data set used to assess skin elasticity, it being understood that the longer it takes for the skin to recover, the less elastic it is. The use of such an instrument on the skin, both before and after product usage, enables quantitative assessment of skin-elasticity efficacy.

Another way to evaluate product claims relating to skin firmness, is a system known as a DynaSKIN®, which is an add-on to the DermaTOP® system, is utilized. This system is completely non-contact and utilizes air that is blown onto the surface of skin at an angle perpendicular to the skin’s surface, to produce a deformation on the skin’s surface that facilitates evaluation of skin firmness. A dedicated software module computes the difference in the degree of skin deformation, both before and after product usage, to determine whether the product is really providing the claimed effect. If the degree of deformation is reduced, then this shows that the product has indeed improved the firmness of the skin. In principle, this system generates both visual and quantitative data in a very reproducible manner that is like the real-world tactile perception of skin firmness, laxity and sag. See, https://www.karger.com/Article/FullText/504063 for additional information.

Skin Smoothness and Anti-Wrinkle Testing
In-vivo testing of these two parameters involves the use of a fringe projection system known as a DermaTOP®. This technique utilizes a fringe projector which shines light onto a person’s skin surface at a certain angle that enables the height and depth if imperfections present on the skin surface to be captured by a camera, specially designed to be used in conjunction with the projector. The images captured by the camera are then evaluated by software that utilizes a specific algorithm designed to measure the height and depth of skin imperfections. When utilizing this technique, the height/depth of skin imperfections are first measured prior to use of the product to establish a baseline reading.

Subsequent measurements are then taken at predetermined time intervals of use to determine what, if any, impact use of the product has had on the previously identified imperfections. If the product is doing its job of making skin smoother and less wrinkled, the height and depth of the imperfections will smaller following use of the product. Perfectly smooth skin, such as may be found on a newborn infant, will have no imperfections. Wrinkled skin, on the other hand, will have imperfections of varying depth and height, which will be detected by the DermaTOP system. By measuring the distance between the height and depth of a wrinkle’s imperfection, both before and after use of a product being evaluated for efficacy, one can quantitatively determine what, if any, effect the product is having on a test subject’s wrinkles. If the measurements show that the height and depth of the wrinkles has been diminished, then the product is deemed efficacious for anti- aging. See, https://www.researchgate.net/publication/230066698_EEMCO_Guidance_for_the_assessment_of_skin_topography for additional information.

Skin Epidermal Thickness
Yet another device typically used to assess the efficacy of an anti-aging product is a Dermascan® C. This device utilizes two-dimensional high-frequency echography to measure the distance between the dermal and epidermal layers of the skin. The device emits an ultrasound beam to generate a two-dimensional image of the space between the dermis and epidermis. This space represents the thickness of the dermis/epidermis junction. As a person ages, their skin naturally becomes thinner and more susceptible to damage. An increase in the thickness of the dermal/epidermal junction causes the skin to appear plumper (younger), thereby confirming a positive anti-aging effect. See, https://pubmed.ncbi.nlm.nih.gov/22772636/ for additional information.

Skin Re-densifying Testing
SIAscopy measures the amount of hemoglobin, melanin, and collagen in the stratum corneum, epidermis and dermis to a depth of 2mm, and identifies whether melanin is present in the epidermis or the dermis. The information is presented as SIAscans which show how these components vary in the skin. SIAscopy makes use of the way light interacts with skin, i.e., the way it scatters or bounces off the skin and the amount absorbed by skin cells and other structures, and how this varies for different wavelengths or colors of light. Due to the multi-layered structure of the skin, and because the most prominent chromophores have slowly varying spectral properties, it is possible to generate models which can predict the method of light transport within skin. This allows analysis of the skin using broadband spectrophotometric techniques. The device used to capture the information is called a SIAscope.

In order to generate the model, simulations are run for hundreds of thousands of different combinations of hemoglobin, melanin, collagen and dermal melanin. The result of each simulation represents how the camera would respond if it were to image the corresponding combination of skin chromophores. This information is then stored and evaluated during each scan in order to generate SIAscans. Each SIAscan is a bitmap representing the concentration of each chromophore on every pixel. Because the use of such intracutaneous spectrophotometric analysis enables collagen content to be measured, a product’s anti-aging benefits can be quantitatively evaluated by taking such measurements before and after product usage. An increase in collagen post-application of product establishes its re- densifying/anti-aging effect. See, https://www.sciencedirect.com/science/article/pii/S0022202X1552664X for additional information.

Skin Radiance
A device known as a C-Cube® is used to measure skin radiance. The device comprises a cutting-edge camera known as a dermascope that is capable of capturing images in Ultra High Definition, i.e., 4K UHD video streaming with 18- million-pixel image resolution and True Color® patented technology that utilizes the full color spectrum when assessing a test subject’s natural skin colors. Once images of the skin are captured, the pixels of the image are converted into standardized colorimetric parameters referred to as L*a*b*. L* stands for clarity (from dark to light), a* stands for the green-to-red color spectrum, and b* stands for the blue-to-yellow color spectrum. The L*a*b* values obtained are then used to generate a radiance score based on a radiance index to assess skin’s lightness, redness and overall homogeneity. The radiance score obtained represents an objective, color-oriented way of measuring changes in skin radiance. When evaluating the radiance effect of a product being tested, radiance scores are taken both before and after product application. An increase in radiance score signifies enhanced skin radiance establishing, objectively, the efficacy of the product being tested. See, https://pubmed.ncbi.nlm.nih.gov/17026656/ for additional information.

UV Protection
When evaluating a product’s photoprotective effect, its ability to inhibit oxidative stress caused by free radicals is measured. The testing protocol involves evaluating three separate samples of a person’s skin: one where the sample has been neither irradiated nor treated (its only purpose is to establish a baseline measurement); one where the sample was irradiated but not treated with product; and one where the sample has been both irradiated and treated. When irradiating skin, the objective is to generate a Minimum Erythema Dose (MED), i.e., the smallest amount capable of causing UV-induced damage which manifests itself in the form of redness (sunburn) to the skin. A xenon solar light lamp with a radiation spectrum of from 290 to 400 (UVA + UVB) is typically used to irradiate the skin. All three skin samples are then biochemically analyzed for the presence of certain biomarkers that represent oxidative stress. These biomarkers include squalene peroxide (SQOOH) which relates to lipid decomposition in the skin; superoxide dismutase (SOD) which is an antioxidant enzyme that protects the body against photo-oxidative damage; catalase (CAT) which is an important enzyme that protects cells against oxidative damage caused by free radicals; and glutathione peroxidase (GPx) a family of enzymes that also protects against oxidative damage. Each of these biomarkers is used to assess the efficacy of a product with regards to UV protection. An increase in the concentration of these biomarkers in skin samples that have been irradiated and treated with product, as compared to those samples that have been irradiated but not treated, evidences the UV protection and/or recovery efficacy of the product in terms of its ability to reduce oxidative stress. See, https://www.nature.com/articles/7701000 for additional information.

Protection Against Environmental Pollutants
Air borne pollutants such as car exhaust, smog and factory exhaust contain dangerous particulate matter which either itself contains free radicals or causes free radical formation when allowed to react within the skin. Free radicals cause skin to experience oxidative stress which affects both its health and appearance. When it comes to evaluating the ability of a product to protect the skin from airborne pollutants, the key criteria include its ability to trap particulate matter on the surface of the skin and how easily the trapped particulate matter can be washed away during cleansing. This analysis involves the use of iron oxide particles (about 1 micron in diameter) which simulate the polluting agent/particulate matter, and a video-microscope fitted with a mobile, fiber optic 20X lens, coupled with an image acquisition computer system to count the quantity of particulates on the skin surface. Iron oxide particles are deposited onto the surface of two small patches of a volunteer’s skin. One patch contains product to be tested, and the other does not. Next, both patches of skin are cleansed with water to determine the amount of particulate matter that is removed. If the amount of particulate matter removed from the treated area is greater than that of the untreated area, the product is objectively proven to be efficacious when it comes to protecting skin from air borne pollutants, i.e., particulate matter.

Dermatologists run clinical trials on over-the-counter (OTC) products by recruiting a group of participants with relevant skin conditions, randomly assigning them to use either the test product or a placebo (control group), and then carefully monitoring their skin over a set period, using standardized assessment tools to measure any changes in their condition, all while following strict ethical and regulatory guidelines to ensure the trial is reliable and unbiased; this typically involves double-blind studies where neither the participants nor the researchers know who is using the test product.

Key points about running OTC dermatology clinical trials:

• Study Design:
  Dermatologists will carefully design the study to address the specific claims made about the OTC product, including the primary endpoint (what they are measuring to assess efficacy) and secondary endpoints (additional measures of interest).
• Participant Recruitment:
  They will recruit participants with the appropriate skin condition that the product is intended to treat, considering factors like age, skin type, and severity of the condition.
• Randomization and Blinding:
  To minimize bias, participants are usually randomly assigned to either the test product or a placebo (a similar-looking product without the active ingredient), and both the researchers and participants are often blinded to which product they are using.
• Assessment Methods:
  Dermatologists use standardized assessment tools to evaluate the skin, including visual grading scales, skin biopsies, and imaging techniques to measure changes in the skin condition over time.
• Data Collection:
  Detailed information about participants' skin conditions, product usage, and any adverse reactions are recorded throughout the study.
• Statistical Analysis:
  After the study period, data is analyzed using statistical methods to determine if
  the test product significantly improved skin conditions compared to the placebo.

Ethical considerations:

• Informed Consent:
  Participants must be fully informed about the study, potential risks and benefits,
  and have the option to withdraw at any time.
• Institutional Review Board (IRB) Approval:
  All clinical trials must be reviewed and approved by an IRB to ensure ethical conduct.
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Dermatologists use graded scales to quantify the severity of a skin disease. These grading system vary by skin condition. We summarize the most widely used here for acne, eczema, psoriasis and rosacea.

Acne
There are multiple grading systems for acne, including the Global Acne Grading System (GAGS), the IGA scale, and the ECLA system:

• Global Acne Grading System (GAGS)
  This system assesses the severity of acne in six areas of the face, chest, and back. The severity is scored on a scale of 0 to 4, with 0 indicating no lesions and 4 indicating nodules. The total score for all six areas is then used to classify the acne severity as mild, moderate, severe, or very severe.
• IGA scale
  The FDA recommends the IGA scale for grading acne. The grades are:

The FDA recommends the IGA scale for grading acne.The grades are:

• 0: Clear
• 1: Almost clear
• 2: Mild
• 3: Moderate
• 4: Severe

• ECLA system
  This system was developed by six French dermatologists and can be used in clinical practice.It is considered reliable, but it is recommended to receive pre-
  training before using it in clinical studies.
• Cook, Centner, and Michaels system
  This system uses a scale of 0 to 8, with photographic standards to illustrate each grade.
• Burke, Cunliffe, and Gibson system
  This system uses a scale of 0 to 10, with 0 indicating no acne and 10 indicating the most severe.

The Dermatology Life Quality Index (DLQI) score is also affected by acne severity, along with other factors like age, acne scars, and postacne hyperpigmentation.

Eczema
There are several dermatology scores for eczema, including theEczema Area and Severity Index (EASI), the Patient Oriented Eczema Measure (POEM), and the
SCORAD:

• Eczema Area and Severity Index (EASI)
  A validated scale that uses a scoring system for redness, thickness, and scratching
  to assess the severity of eczema in patients over 8 years old.The EASI score ranges from 0 to 72 points, with higher scores indicating more severe eczema. The severity of eczema based on the EASI score is categorized as follows:

• 0 = clear
• 0.1 to 1.0 = almost clear
• 1.1 to 7.0 = mild
• 7.1 to 21.0 = moderate
• 21.1 to 50.0 = severe
• 50.1 to 72.0 = very severe

• Patient Oriented Eczema Measure (POEM)
  Uses a banding system to help patients and clinicians understand their eczema
  severity:

• 0 to 2 = clear or almost clear
• 3 to 7 = mild eczema
• 8 to 16 = moderate eczema
• 17 to 24 = severe eczema
• 25 to 28 = very severe

• SCORAD
  The score for each area is added up, with the total area having a possible maximum of 100%. Digital tools are also available to help assess eczema severity.

Psoriasis
The Psoriasis Area and Severity Index (PASI) is a widely used dermatology score to assess the severity of psoriasis and a patient's response to treatment:

• Scoring
  The PASI score ranges from 0 to 72, with higher scores indicating more severe psoriasis.
• Calculation
  The PASI score is calculated by assessing the severity of lesions in four body regions: head and neck, upper limbs, trunk, and lower limbs. The severity of each region is assessed for erythema, induration, and scaling on a scale of 0 to 4. The extent of psoriatic involvement in each region is also graded on a scale of 0 to 6. The body area scores are then multiplied by the area affected.
• Interpretation
  A PASI score of 0 to 5 indicates none to mild psoriasis, 6 to 10 indicates moderate psoriasis, and 11 or above indicates severe psoriasis.
• Clinical use
  The PASI is used in clinical trials to assess the effectiveness of new psoriasis treatments. The benchmark for most clinical trials is a 75% reduction in the PASI score.

Rosacea
There are several ways to score rosacea, including:

• Rosacea Area and Severity Index (RASI)
  A score from 0 to 72, with higher scores indicating more severe rosacea. The RASI evaluates rosacea features in four facial areas, adjusting for the relative importance of each area.
• Investigator Global Assessment (IGA)
  A five-point scale from 0 to 4, with higher scores indicating more severe rosacea. The IGA is a global evaluation that doesn't consider each lesion type or affected area separately.
• Grading system
  Clinicians may grade primary signs and symptoms as absent, mild, moderate, or severe (0-3). Secondary features may be graded as absent or present.
  Rosacea is diagnosed based on a patient's medical history and the appearance of their skin and eyes. A doctor may order tests to rule out other conditions that look like rosacea.

1. https://pubmed.ncbi.nlm.nih.gov/19514927/
2. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3842001/
3. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4969411/
4. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4268288/
5. https://www.researchgate.net/publication/314923242_Measurement_of_Skin_Surface_Hydration
6. https://pubmed.ncbi.nlm.nih.gov/29923639/
7. https://pubmed.ncbi.nlm.nih.gov/30348333/
8. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4730153/
9. https://pubmed.ncbi.nlm.nih.gov/26114451/
10. https://www.researchgate.net/publication/232430355_EEMCO_Guidance_for_the_in_vivo_Assessment_of_Skin_Greasiness
11. https://www.karger.com/Article/FullText/504063
12. https://www.researchgate.net/publication/230066698_EEMCO_Guidance_for_the_assessment_of_skin_topography
13. https://pubmed.ncbi.nlm.nih.gov/22772636/
14. https://www.sciencedirect.com/science/article/pii/S0022202X1552664X
15. https://pubmed.ncbi.nlm.nih.gov/17026656/