Urban particulate matter in air pollution penetrates into the barrier-disrupted skin and produces ROS-dependent cutaneous inflammatory response in vivo

Anti-pollution or anti-particulate matter has become a huge buzzword in cosmetics. Pollution and particulate matter have been linked to many negative health effects (mainly cardiovascular) and while the link to skin health and acceleration of ageing are logical…does the data support it?

There have a been a few correlational studies that have shown that people living in areas with higher levels of pollution exhibit more signs of oxidative stress in skin lipids and some have even correlated it with increased wrinkling. But what’s the mechanism and can particulate matter even penetrate the skin?

A group of researchers from Seoul used an in vivo mouse and in vitro keratinocyte model to study this.

First was the collection of particulate matter from the air. To do this they set up a vinyl tarp on a rooftop near a busy intersection to collect dust. The particulate matter was then purified and separated to be used in the experiment. The majority of the particles ranged from 200 to 300 nm. Particulates found included: Naphthalene, biphenyl, acenaphthylene, acenaphthene, fluorene, dibenzothiophene, and 28 others identified.

For the in vitro portion of the experiment, cell cultures of human primary keratinocytes were performed with varying concentrations of the particulate matter. The cells absorbed the particulate matter, and the researchers found a concentration-dependent increase of inflammatory cytokine IL-8 and collagenase MMP-1. They also found that the addition of an antioxidant, n-acetyl cysteine, was able to suppress this effect.

In the in vivo portion of the experiment, the researchers used mice that did not produce melanin and divided them into two skin conditions: One with their skin intact, and another with barrier-damaged skin. To damage the skin barrier they stripped the skin 10 times with tape to remove layers of the stratum corneum. The particulate matter was applied 10 times over 2 weeks and included a skin penetration enhancer (DMSO).

While the in vitro results may be “scary”, the in vivo results were milder. Particulate matter was shown to penetrate into the intercellular space of the barrier-disrupted mice, but not the intact mice. Particulate matter was found in hair follicles of both, but there was no epidermal penetration of the particulate matter in the intact mice.

The researchers did find an increase in inflammation in the particulate matter treated skin compared to skin not exposed- whether or not the sin was intact or tape-stripped. However, the inflammation was much more severe in the tape-stripped group. The researchers also showed that intradermal n-acetyl cysteine was able to ameliorate the increase in inflammation caused by particulate matter, but they did not perform this portion of the experiment on the intact mice. It’s likely this same treatment will have a similar effect in the intact mice, but it is unknown.

The researchers also point out some issues with their own experiment: The concentration of particulate matter may not reflect the amount that a person would be exposed to and that their sampling of particulate matter had a high concentration of sulfur which may be unique to their location. It’s also important to remember that mice are not humans, and we may react differently.

While it’s likely that the addition of anti-inflammatories and antioxidants may help attenuate some of the potential inflammation caused by pollution and particulate matter, it’s unknown which chemicals and what combinations are most effective for humans. There’s also no standard measurement to gauge a protective effect so it is impossible to compare one product to another. Again, we see another case of the marketing being ahead of the science.

Source: Jin Seon-Pil, Li Zhenyu, Choi Eun Kyung, Lee Serah,
Kim Yoen Kyung, Seo Eun Young, Chung Jin Ho, Cho Soyun.Urban particulate
matter in air pollution penetrates into the barrier-disrupted skin and produces ROSdependent
cutaneous inflammatory response in vivo.Journal of Dermatological Science
https://doi.org/10.1016/j.jdermsci.2018.04.015

#BeautyRecap: July 11th, 2018

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Urban particulate matter in air pollution penetrates into the barrier-disrupted skin and produces ROS-dependent cutaneous inflammatory response in vivo
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#BeautyRecap: July 3rd, 2018

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#BeautyRecap: June 26th, 2018

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Our judgement is influenced by conflict of interest
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#BeautyRecap: June 19th, 2018

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2-methoxymethyl-para-phenylenediamine containing hair dye as a less allergenic alternative for para-phenylenediamine allergic individuals
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Widespread regular sunscreen application deemed not useful in the U.S.A.
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Deep learning-based, computer-aided classifier developed with a small dataset of clinical images surpasses board-certified dermatologists in skin tumor diagnosis
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Widespread regular sunscreen application deemed not useful in the U.S.A.: reply from authors
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Why a randomized melanoma screening trial is not a good idea
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The global prevalence and correlates of skin bleaching: A meta-analysis and meta-regression analysis
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Polyamine regulator AMD1 promotes cell migration in epidermal wound healing
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Dermal fibroblast SLC3A2 deficiency leads to premature aging and loss of epithelial homeostasis
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The in vitro antimicrobial evaluation of commercially essential oils and their combinations against acne
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Colour differences in Caucasian and Oriental women’s faces illuminated by white light‐emitting diode sources
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Human skin‐depigmenting effects of resveratryl triglycolate, a hybrid compound of resveratrol and glycolic acid
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Validation of an in vitro sun protection factor (SPF) method in blinded ring‐testing
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A population ‐based cohort study of atopic eczema among young adult males in Singapore
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Skin penetration of Vitamin C (Ascorbic acid): Part II

“Applying 15% Vitamin C for three consecutive days creates a reservoir effect in the skin.”

Firstly, I want to remind you that this study was done on pig skin – not humans. The way that ascorbic acid is stored and metabolized in pig skin may vary from human skin.

Most animals, like pigs, are able to synthesize their own ascorbic acid from glucose, but humans cannot. It’s possible that this data from pigs will be similar to human data, but it’s also very possible that it won’t be. Neither has been proven yet. Presenting an assumption as truth is misleading – but often done in marketing.

I also want to remind you that the way that the ascorbic acid was applied to the skin was not the same way that we apply our skincare. In these experiments, the ascorbic acid solution was applied with a Hill Top Chamber, which occludes the skin, reducing evaporation and theoretically enhancing skin penetration.

For this part of the experiment, Pinnell and his group applied a 15% ascorbic acid solution at pH 3.2 to pig skin for 5 days with a Hill Top Chamber. After the 5th day, application of the ascorbic acid was stopped and ascorbic acid levels in the skin were monitored for an additional 5 days.

After the 3rd day of application of the ascorbic acid serum, the ascorbic acid levels in the skin do appear to reach a peak around 1100 pmol/mg. The deviation around the mean does appear to be reducing with each further day between the 3 subject pigs.

We do need to consider if this theoretical peak amount of ascorbic acid is reached in real-life situations. The living conditions of the pigs in the study were not described, so it’s possible that they were not exposed to natural daylight. It’s understood that UV exposure reduces the amount of ascorbic acid in the skin. UV increases the production of free radicals in the skin, and ascorbic acid is part of the natural antioxidants in the skin which help neutralize these free radicals.

In an experiment using human skin models, it was found that exposure to 16.9 joules/cm² (About 12 minimal erythemal dose equivalent) of UV reduced ascorbic acid levels in the skin model by almost ⅓. This was a higher amount of UV exposure the experimenters expected, they were also unable to detect dehydroascorbic acid in the skin. The study does have some issues which “may be explained by the high levels of ascorbate present in the [tissue] medium…added by the manufacturer to increase collagen synthesis”.

“Vitamin C remains in the skin for 3-4 days and doesn’t wash out”

This marketing claim may be due to some confusion of the term “washout”. In drug experiments a “washout period” refers to the period of time when treatment is stopped, it does not necessarily mean that the skin is washed out.

After applying the 15% ascorbic acid solution to the pig skin, they discontinued application and monitored ascorbic acid levels in the skin. Unfortunately, the methodology in this portion of the experiment isn’t explicitly described. It is unclear, for example, if the pig’s skin was washed each day. The washing procedure is described as “…at the end of the experiment, the formulation was washed vigorously from the skin with water.”

Because most of us use surfactant based cleansers to wash our skin, this data may not be as applicable as the pig’s skin was washed with only water. However, the pig’s skin was removed of stratum corneum before ascorbic acid measurement and the lower layers of skin are likely less affected by the washing and surfactant based-cleanser.

Based on this data, the half-life (the amount of time it takes for the detected ascorbic acid levels to drop by half) was estimated at around 4 days. But as mentioned above, it’s unclear what the living conditions of the pigs were and whether or not they were exposed to sunlight which reduces antioxidant levels in the skin.

Can Vitamin C derivatives increase levels of Vitamin C in skin?

The last portion of the Pinnell experiment looked at whether or not the topical application of Vitamin C derivatives could increase levels of Vitamin C as ascorbic acid in pig skin.

For 24 hours, solutions of dehydroascorbic acid, 10% ascorbyl-6-palmitate, 12% magnesium ascorbyl phosphate, and 15% ascorbic acid were applied to pig skin. Compared to control, only the 15% ascorbic acid solution created a statistically significant increase in ascorbic acid levels in the skin.

For the derivatives, there was no statistically significant difference between the application of the derivative and control (no application of derivatives or Vitamin C) – which implicates that, at least for pig skin, these specific derivatives do not convert to Vitamin C.

For the solutions of dehydroascorbic acid, pig skin levels of ascorbic acid were 7.51 ± 3.34 pmol/mg for 20 mM dehydroascorbic acid and 8.70 ± 2.13 pmol/mg for 1 M dehydroascorbic acid. Where no dehydroascorbic acid was applied levels of ascorbic acid were 9.24 ± 3.55 pmol/mg.

In conclusion…

It surprises me how influential this one study on ascorbic acid applied to pig skin has become in terms of marketing language for brands.

Even later studies with Dr. Pinnell as an author leave out that the data are collected from pig skin, “Following topical application, once the skin is saturated with L-ascorbic acid, it remains with a half-life of about 4 d (Pinnell et al, 2001).”

While this experiment is some of the best data we have in terms of ascorbic acid penetration based on formulation, the key point to remember is that human skin cannot be assumed to behave the same as pig skin.

So if you see a claim similar to “15% Vitamin C at pH 3.5 is the most effective concentration”, please imagine me beside you whispering “…for pigs”.

Edit: An error was made in the original version published, pigs can synthesize Vitamin C from glucose, but humans can not. Guinea pigs also cannot synthesize their own Vitamin C.

Edit: An error was made in the original version published, pmmol was corrected to pmol.

Source: Pinnell, S. R., Yang, H. , Omar, M. , Riviere, N. M., DeBuys, H. V., Walker, L. C., Wang, Y. and Levine, M. (2001), Topical L‐Ascorbic Acid: Percutaneous Absorption Studies. Dermatologic Surgery, 27: 137-142. DOI: 10.1046/j.1524-4725.2001.00264.x

Podda, M., Traber, M.G., Weber, C., Yan, L., Packer, L. (1998), UV-Irradiation Depletes Antioxidants and Causes Oxidative Damage in a Model of Human Skin, Free Radical Biology and Medicine, 24: 55-65. DOI: 10.1016/S0891-5849(97)00142-1