La Paraffina cosmetica è comedogenica ? l’opinione di J.C.DiNardo

Su una rivista che ho spesso consultato,Journal of Cosmetic Dermatology, anni fa è comparso un articolo di un ricercatore che ha pubblicato molti papers relativi alla cosmesi.

Assieme alla Draelos ha anche proposto una revisione del concetto di comedogenicità e protocolli di test su volontari umani che superassero le valutazioni con test su animali definite nel metodo Mills – Kligman.

Premesso che la potenziale comedogenicità deve essere comunque valutata sul cosmetico finito e non su un suo ingrediente è interessante notare come  su un ingrediente discusso come il PARAFFINUM LIQUIDUM  avremmo l’ennesima ricerca che conferma come la conclamata e paventata comedogenicità sia una bufala.
Perché tra tante ricerche copio e incollo questa ? Perché mi piace come affronta il problema del rapporto tra ricerca scientifica e marketing.
What is the message? Don’t be fooled by marketing claims.

 

DiNardo, J. C. (2005). Is mineral oil comedogenic? Journal of Cosmetic Dermatology, 4(1), 2–3. doi:10.1111/j.1473-2165.2005.00150.x

The phrase, “acne cosmetica” was coined in the early 1970s to describe the association between cosmetic use and acne breakouts in women over the age of 30. Cosmetic formulations at that time did contain a number of animal, mineral, and vegetable oils, as well as synthetic oils (esters) which were thought to clog pores and perhaps elicit the response. A number of methods were quickly developed to evaluate the comedogenic potential of these ingredients, and several of these were found to evoke a response in the rabbit’s ear. This quickly became the model of choice. Several years later, a human model was developed, and researchers noted a difference between the results. Several ingredients elicited less of a comedogenic response. At this point in time, a great deal of confusion in interpreting comedogenic results existed. Both dermatologists and those in the cosmetic industry were unsure of the significance, if any, that the reported data held with respect to “acne cosmetica.” In an attempt to understand the contrasting results between the animal and human models, the American Academy of Dermatology (AAD) held an international symposium on comedogenicity.1

Several factors were taken into account (methodology, experimental design, results obtained, etc.), and based on the data presented, the symposium concluded that “if the animal model does not show evidence of comedogenesis, the test material under consideration is unlikely to be comedogenic in human skin. One-plus reactions are also unlikely to cause reactions in humans. Two-plus or three-plus responses require sound scientific judgment. Reformulation should be considered or the product should be adequately tested in humans before general use.” It should be noted that the comedogenic grades used in this statement are based on a 0 (no activity) to 3 (severe activity) scale, and that researchers were reporting results using a 0 (no activity) to 5 (severe activity) scale. Therefore, when interpreting the reported data, the AAD-recommended values would have to be shifted to include a one-plus to a two-plus for “unlikely to be comedogenic” and grades three-plus to five-plus “would require reformulation or adequate testing in humans.”

So, “is mineral oil comedogenic?” This is a question that physicians, estheticians, cosmetic marketers, and consumers have asked me several times a year for the last two decades. Looking over the animal data that have been generated over the years (published2–5 and unpublished) using the rabbit ear model, mineral oil elicits a comedogenic grade ranging from 0 to 2 on a 5-point scale (Table 1). Taking into account the AAD recommendations, mineral oil would be categorized as “unlikely to be comedogenic in human skin.” To determine if this conclusion could be considered accurate, a number of finished products containing mineral oil were evaluated using the human model. These products ranged in mineral oil concentration from approximately 0.5% to 30%. The testing was conducted as outlined by Mills and Kligman.6 However, in order to avoid a subjective grading, the mean ratio of follicles to microcomedones was obtained for both pre-application and postapplication sites, and a percent change from baseline was calculated to determine the degree of microcomedone formation. This allows the data to be expressed in the form of a percent, yielding a clearer picture of the comedogenic activity. The data depicted in Table 2 presents the percent change in microcomedone activities for the products tested (9–34%). The percent change from baseline is within the normal range of ±10% of the negative control (15–30%) tested and can therefore be considered noncomedogenic in humans. Additionally, based on the 85–95% change in microcomedone activity noted for the positive control (octyl palmitate or INCI name ethylhexyl palmitate), it would appear that this material does exhibit a comedogenic response when tested undiluted in humans.

So, “is mineral oil comedogenic?” No, based on the animal and human data reported, along with the AAD recommendation, it would appear reasonable to conclude that mineral oil is noncomedogenic in humans. Will we see more products containing mineral oil in the market? No, marketing claims have convinced us that mineral oil is a comedogenic ingredient and it will be far too hard for anyone to convince the consumer, after being bombarded by mineral-oil–free claims for decades, that it is now okay to use products that contain mineral oil.

What is the message? Don’t be fooled by marketing claims. Although it is very difficult to find the time to research the numerous claims that are thrown at us daily, look for products that have been tested and claim to be noncomedogenic as opposed to just looking at the ingredients listed on the box or “ingredient x-free” statements. As with all toxicological testing, the effects observed when testing an actual product in humans is the best form of assessment to determine potential hazards associated with any ingredient and/or product.


Table 1 Reported comedogenic activity of mineral oil in animals.

Test ingredient/grade Reported comedogenic activity (conc. tested)*
Mineral oil/carnation 0 (100%)
Mineral oil/light 1–2 (100%)
Mineral oil/medium 0–1 (100%)
Mineral oil/heavy 0 (100%)
Mineral oil/technical 1 (100%)
Mineral oil/not specified 0–2 (10% in Propylene Glycol)

*Values reported are based on a 0 “no activity” to 5 “severe activity” scale.


Table 2 Comedogenic potential of products containing mineral oil.

Product type Mineral oil range % change from baseline*
Body scrub 0.5–1% 12%
Foot cream 1–5% 9%
Hand and body cream 5–10% 13%
Facial cleanser 5–10% 33%
Facial moisturizer 5–10% 13%
Powder face make-up 10–25% 8%
Pressed face powder 25–30% 34%
Negative control N/A 15–30%
Positive control N/A 85–95%

*Percent change from baseline is based on the change in microcomedone to follicle rations for pre- and post-treatment.


References

1 American Academy of Dermatology invitational symposium on comedogenicity. J Am Acad Dermatol 1989; 20: 272–7.

2 Fulton JE. Comedogenicity and irritancy of commonly used ingredients in skin care products. J Soc Cosmet Chem 1989; 40: 321–33.

3 Kligman AM, Kwong T. An improved rabbit ear model for assessing comedogenic substances. Br J Dermatol 1979; 100: 699–702.

4 Lanzet M. Comedogenic effects of cosmetic raw materials. Cosmetics & Toiletries 1986; 101: 63–72.

5 Morris WE, Kwan SC. Use of the rabbit ear model in evaluating the comedogenic potential of cosmetic ingredients. J Soc Cosmet Chem 1983; 34: 215–25.

6 Mills OH, Kligman AM. Human model for assessing comedogenic substances. Arch Dermatol 1982; 118: 903–5.

Rodolfo Baraldini

pubblicato 14 dicembre 2013

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2 Commenti

  1. Lo studio è interessante benché non sia la mia materia. E’ giusto non farsi influenzare dal marketing anche quando questo verta al ” naturale” e ” free…”, perché è pur sempre una tecnica di vendita. Ma resta il dubbio sul perché molti abbiano notato la differenza sull’utilizzare o meno paraffina. Personalmente ad esempio sulla pelle non ho trovato differenze di portata rilevante ( qualche comedone in meno ma non ho una pelle di pesca), ma sulle labbra sì, trasformate. Effetto placebo?

    • L’effetto che ha una sostanza sulla pelle è indipendente dalle sue origini, in sostanza che sia petrolifera, di sintesi , biologica o vegetale non fa differenza. Gli alkani che compongono le paraffine petrolifere o vegetali che siano hanno una buona emollienza ed una buona occlusione cutanea . Contrariamente a quello che si pensa l’occlusività di un emolliente non è un parametro negativo a priori e non centra con la comedogenicità. Infatti la occlusività cutanea in cosmesi si misura in termini di riduzione della perdita di acqua, in sostanza riduzione della perdita di idratazione. Quindi più una sostanza è occlusiva , più “idrata” la pelle. Le paraffine sono occlusive ma non sono le migliori sostanze con questa caratteristica. Ci sono molti grassi vegetali e soprattutto miscele di sostanze, con una occlusività cutanea maggiore, quindi con una idratazione indotta, migliore delle paraffine. Per questo e per altre ragioni simili non c’è nulla di strano nel poter rilevare che alcuni cosmetici senza paraffine, si comportano “meglio”, cioè sono più occlusivi, di cosmetici con paraffine.Detto questo non si può comunque generalizzare, Infatti a parte la variabilità della risposta soggettiva, ogni formulazione cosmetica fa storia a se e la presenza in etichetta di un ingrediente anzichè di un ‘altro pesa sul risultato e sull’efficacia finale in modo molto relativo.

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