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How to Read Skin Care Research Studies

We have all heard that we should use evidence-based skin care products, but how do you know if skin care products really work if you don’t know how to read the skin care research in a scientific research publication? I will review how to read skin care research articles and evaluate the effectiveness of skin care products based on research articles on skin care products.

Evaluating cosmeceutical research trials, especially anti-aging ingredient research, can be difficult.  There are many new cosmeceutical ingredients every year with research studies to support their use. I perform research trials in my dermatology practice in Miami Florida, so I am going to tell you how to evaluate research data and read research studies.

Cosmeceutical Claims

Data and marketing claims on cosmeceutical ingredients are intentionally vague and difficult to comprehend because cosmetics are not allowed to make any claims that cosmetic ingredients affect the skin’s biology.  They are only allowed to “affect the appearance of the skin” but not change the underlying biology of the skin.  In other words, technically cosmetic companies are not allowed to claim that their products increase collagen production or turn on or off specific biologic pathways.  Of course many do. I personally think companies should be allowed to openly disclose their research findings because otherwise it is too easy for cosmetic companies to exaggerate their claims and not back them up by science.

Skin Care Research Article Abstracts

The abstract of the research publication that discusses the trial results is the section most reviewed by readers.  It is easily seen on Google Scholar and PubMed without a fee. The statements in the abstracts can be misleading by leaving our important information.  Companies know you probably won’t read the entire study so there are tricks they use.  Remember, many times the purpose of these studies is to back up exaggerated marketing claims, so the marketing people may help write these extracts.  Read them carefully.

Read the Entire Cosmetic Research Study

It is always necessary to read the entire study.  Do not accept the statements made in the abstract at face value.  Be cynical and look for how they might be exaggerating the results.

 The Quality of the Medical Journal Matters

Just because something is published in a scientific journal, does not mean it is a good research trial.  In fact, in the last decade, many poor medical journals have emerged as a business.  They charge high fees to publish data and skimp on the review process allowing poor research to get published.  Substandard medical journals allow publication of incorrect hypotheses and flawed data.  This is why if you consider yourself an expert on skin care, you must learn to read medical publications like a scientist.

The best studies are published in peer-reviewed journals that have a high impact factor.

Peer reviewed

Peer reviewed means that recognized experts unaffiliated with the study have reviewed the article and agreed with the study design and the conclusions of the study. Although the data published in these journals is considered more credible, you should still carefully read the entire article.

Impact factor (IF)

The impact is a measure of the importance and credibility of a scientific journal based on the frequency with which the average article in a journal has been cited as a reference in the previous two years. The impact factor of the article that cites the reference is also taken into consideration.  In other words, if the most reputable journals reference Journal X many times, this increases the impact of Journal X.

The Credibility Of The Investigator

The reputation and background of the researcher matters too.  You can look up a researcher on researchgate.net and see their “research interest score” and how many time their research has been cited.  This can give you an idea of the expertise and reputation of the lead investigator in the cosmetic research study.

What Are The Best Medical Journals in Dermatology?

The highest impact journals in science include:

• The New England Journal of Medicine
• The Lancet
• Nature
• Science

The highest impact factor journals in dermatology are:

• Journal of the American Academy of Dermatology,
• British Journal of Dermatology
• Journal of Investigative Dermatology.

Google Scholar displays results so that the highest impact articles are at the top of search results. This is why it is better to search for cosmeceutical skin care research trials on Google.scholar.com or Pub Med, the National Library of Medicine’s website, than on Google.com.  Google Scholar is easier to navigate and links to the publication on Pub Med, so I prefer Google scholar.

On Pub Med and Google Scholar, the abstract of the article will appear, but access to the entire content may require a fee. The abstract can be misleading, especially in low-impact journals.

Evidence based Antiaging Skin Care Ingredient Research Studies

The anti-aging cosmeceutical research segment probably has the most misleading research trials of all.  There are many good evidence based skin care research trials, but you need to know how to recognize the good from the bad studies.

Which antiaging ingredients have the best evidence based research studies?

• Retinoids are the most studied, most proven compounds for aged skin (2)
• Ascorbic acid has many studies showing it increases collagen synthesis
• Exosomes have interesting data but studies on the effects on skin are just emerging
• DNA Repair enzymes have convincing data

Cell cultures, animal data and human data in cosmetic trials

Most cosmetic ingredients will have cell culture or bioengineered skin equivalent data because animal studies are not performed very often anymore. It is always important to see how the skin care studies were performed:

• in vivo (on animals or humans)
• in vitro (cell cultures)
• On bioengineered skin equivalents
• On animals
• On human
• The Franz cell skin permeability assay (3)

If the data is from cell cultures, determine if they are keratinocytes, fibroblasts, or other types of cells. Keratinocytes are the cells that make up the epidermis and fibroblasts are the cells that make up the dermis. Cell culture data on cosmeceuticals is less convincing. Remember- penetration of the skin care ingredient into the dermis is important for antiaging results.  Using a cosmetic ingredient in cell cultures bypasses the need for penetration.  This is why studies on peptides look so good in cell culture, but peptides don’t perform well on human skin. (They are not stable and do not penetrate). The Franz cell skin permeability assay is a good study to determine if cosmeceutical ingredients can penetrate into the dermis.  This assay uses excised skin applied over a closed container.  The ingredients are to applied on the epidermal side or the skin and then measurements are made inside the container to see if the ingredients were able to pass thru the skin.  However, the skin is not quite the same as live skin because it is either cadaver skin or bioengineered skin which is not exactly the same as living human skin.

Study Design

When evaluating human cosmeceutical studies, study design should be assessed. Studies can be:

• Open label
• Single blind
• Double blind
• Placebo controlled
• Vehicle controlled

A double-blind controlled study in which the subject and the evaluator do not know who received the study cosmeceutical and who received the control (vehicle or placebo) is the most convincing study design. It is difficult for bias to play a role when the investigators and the subject do not know which is the active ingredient and which is the control.  However, most cosmeceutical skin care trials are open label and not blinded or placebo controlled which allows for bias. 

Control group- Use of placebo, vehicle, or nothing

In many skin care trials, a cosmeceutical is compared to using nothing, which makes it easy to reveal the cosmeceutical as superior to the control. For example, the moisturizing capabilities of the product will render the skin smoother as compared to unmoisturized skin. So using any moisturizer at all versus no moisturizer will always show superiority of the moisturizer.  A properly designed study would compare a moisturizer with an active ingredient versus a moisturizer without an active ingredient. The moisturizer without an active ingredient is called a vehicle.  Studies that utilize this method are called vehicle controlled rather than placebo controlled.

Wash out period

The washout period prior to the study is when any products that will affect the results of the trial are discontinued.  In skin care trials, the washout period is usually two weeks. Look at see what products were used in the wash out period. 

Tricks used in open label trials to make the results seem better than they are. For example-

In the washout period the subjects are not allowed to use any skincare products on the face- not even moisturizers.

• This dehydrates the skin
• This allows for buildup of dead stratum corneum (SC) cells
• The skin looks rough and dull
• The skin poorly reflects light
• The skin develops textural fine lines.
• These conditions are ideal for “before” photos.

In this situation, any type of humectant, emollient, occlusive, or exfoliating ingredients will yield quick improvement in textural changes and light reflection and the skin will look better just by being hydrated and exfoliated.  This study design is used often in cosmeceutical studies that appear to show improvement of wrinkles in hours to seven days. Wrinkles do not improve this quickly and the desquamation keratinization cycle is much longer! True wrinkles take months to clear.

Length of Time of the Study

Most skin care studies are 12 weeks. Melasma studies are usually 16 weeks. Any anti-aging skincare studies that evaluate fine lines and wrinkles would optimally last at least four months on human skin; however, six months to a year would be more convincing.

Use of biopsies in studies

Studies often include biopsies before and after a product is applied to render a qualitative measure of collagen content. (5) This is problematic because the act of wounding with a biopsy triggers a wound healing response that increases collagen content. The best studies take the “after” biopsy form a different place on the body.  For example, the before biopsy would be on one arm and the after biopsy would be on the other arm.

Measurements used in skin care research studies

Quantitative outcomes such as gene expression, RNA, or protein expression are preferred, but these methods are expensive.

The most commonly used measurements in skin care trials are:

• Cutometer measures elasticity
• Tewameter and Corneometer measure skin hydration
• Spectrophotometer measures color (red and brown)
• Mexameter measures brown (Presence of melanin)
• Photography- the most commonly sued the Canfield Visia System
• Silicone casts- measure wrinkles on the skin’s surface

Statistical Significance

Data is reported as “statistically significant” or “not statistically significant” based on P-values. For statistical significance, the P-value must be < 0.05. If not, it means that it cannot be concluded that a significant difference exists between the groups. Studies should always report the P-value when giving data. Be suspicious if they do not because when there is a significant difference, it is proudly stated in the article’s abstract. If the P-value is not provided, it usually means it was >0.05. When this is the case, analyze the data carefully.

Example of a well designed evidence based skin care study:

The landmark studies on tretinoin for photoaged skin in 1993 evaluated photoaged skin treated with tretinoin for 10 to 12 months. (4) Take a look at this trial to see what a good one looks like.

Skin care experts need to develop their scientific knowledge to decipher skin care claims. This article just scratches the surface of how to read a research study, but even knowing this small amount will make you a more discerning skin care enthusiast than most people.

References:

1. Baumann L. Antiaging Ingredients in Baumann’s Cosmetic Dermatology Ed. 3 (McGraw Hill 2022) 
2. Fisher, G. J., Talwar, H. S., Lin, J., & Voorhees, J. J. (1999). Molecular mechanisms of photoaging in human skin in vivo and their prevention by all‐trans retinoic acid. Photochemistry and photobiology, 69(2), 154-157.
3. Franz, T. J., Lehman, P. A., & Raney, S. G. (2009). Use of excised human skin to assess the bioequivalence of topical products. Skin pharmacology and physiology, 22(5), 276-286.
4. Griffiths, C., Russman, A. N., Majmudar, G., Singer, R. S., Hamilton, T. A., & Voorhees, J. J. (1993). Restoration of collagen formation in photodamaged human skin by tretinoin (retinoic acid). New England Journal of Medicine, 329(8), 530-535.
5. Osman, O. S., Selway, J. L., Harikumar, P. E., Stocker, C. J., Wargent, E. T., Cawthorne, M. A., … & Langlands, K. (2013). A novel method to assess collagen architecture in skin. BMC bioinformatics, 14(1), 260.

October 7, 2022