Friday, April 20, 2012

Chemistry of our skin: pH of our skin

I've found such an assortment of really interesting papers on the pH of our skin, I had to share them with you! The writing in purple is the text from the study with my comments before and after.

What is the proper pH of our skin? As I've written in the past, the general range is considered around pH 5.4 to 5.9, but this is based on the surface of the lower arm of the Caucasian male. There are variations depending upon skin type, skin colour, gender, and so on.

This paper notes: A statistically significant difference in skin pH between men (mean pH= 5.80) and women (mean pH=5.54) was found, with women being more acidic than men (P<0.01)...Spontaneous skin surface pH was found to be significantly lower in women, as compared to men - albeit, the difference was small and of unknown relevance.

So women tend to be slightly more acidic than men, but it doesn't seem to be a big deal. Okay, great. Let's take a look at another study about the average pH of our skin!

Variable skin pH values are being reported in literature, all in the acidic range but with a broad range from pH 4.0 to 7.0. In a multicentre study, we have assessed the skin surface pH of the volar forearm before and after refraining from showering and cosmetic product application for 24h. The average pH dropped from 5.12 ± 0.56 to 4.93 ± 0.45. On the basis of this pH drop, it is estimated that the ‘natural’ skin surface pH is on average 4.7, i.e. below 5. This is in line with existing literature, where a relatively large number of reports (c. 50%) actually describes pH values below 5.0; this is in contrast to the general assumption, that skin surface pH is on average between 5.0 and 6.0. Not only prior use of cosmetic products, especially soaps, have profound influence on skin surface pH, but the use of plain tap water, in Europe with a pH value generally around 8.0, will increase skin pH up to 6 h after application before returning to its ‘natural’ value of on average below 5.0. It is demonstrated that skin with pH values below 5.0 is in a better condition than skin with pH values above 5.0, as shown by measuring the biophysical parameters of barrier function, moisturization and scaling. The effect of pH on adhesion of resident skin microflora was also assessed; an acid skin pH (4–4.5) keeps the resident bacterial flora attached to the skin, whereas an alkaline pH (8–9) promotes the dispersal from the skin.
(From this paper.)

The people studied were from The Netherlands: 167, Germany: 87, The Philippines: 40, Spain: 36. In my humble opinion, this isn't really enough of a cross section of the different skin types around the world to make a definitive statement. If you read further into the paper, you'll see they address this issue.

Their conclusion is that our skin is about pH 4.7, which is more acidic than we thought! The concept of skin having a pH of 5.4 to 5.9 seems to come from skin that has been exposed to skin care products.

So why do we care about the pH of our skin? 
The surface of the skin is covered with a protective acidic hydrolipid film with pH 4.5-5.5. This is the emulsion of substances dissolved in water, composed of sebaceous and sweat gland secretion and products of decomposed corneocytes, whose bactericidal and fungicidal properties are based on mild acidity. Additionally, this emulsion prevents evaporation of water from the surface of the skin, which contributes to the maintenance of stratum corneum hydration...pH values of the skin surface significantly influence microflora and, by protecting from penetration of microorganisms into the body, also influence the skin barrier function. Increased pH values reduce the antibacterial and antimycotic properties of the skin surface, which enables more frequent occurrence of infections. (From this paper.)

In other words, if the pH of our skin gets higher than normal, the ability of our skin to protect us from bacteria and yeast will be reduced and we'll get more of those kinds of infections.

[S]ubjects with skin pH < 5.0 show statistically significant less scaling and higher hydration levels than subjects with skin pH > 5.0 (this paper).

In other words, people with less acidic skin tend towards what we would call dry skin with more scaling (skin flakes) and lower hydration levels.

It is interesting to mention in this respect that competent lipid barrier formation in neonatal skin and barrier repair of damaged skin are delayed at neutral pH conditions. Furthermore, regeneration of barrier function after damage with acetone or extensive tape stripping proceeds significantly faster when the skin is exposed to acidic pH (5.5) than neutral pH (c. 7.2), indicating that barrier formation and restoration (both in mice and in humans) is a process stimulated by low pH as well as a steep pH gradient. (From this paper)

In other words, acidic pH levels our skin good, neutral possibly not great, alkaline bad.

So why do we care about any of this? Well, that seems like a silly question considering we're making our products to help with things like dry skin, that feeling of tightness after washing one's hands, and other things of that nature. We can alter the pH of our skin by using various products...which sounds like an interesting post for tomorrow!

9 comments:

Anonymous said...

I've read various things about how different acids are good for skin, but mostly either they're chemically exfoliating, or adding vitamin c.

So learning about how important it is to have slightly acidic skin was interesting and cool, thanks. I look forward to tomorrow's post.

Also, would it be OK to alter certain commercial products to make them more acidic? I'm wondering if that's a more complex question than I meant for it to be.

Thanks,
Shreela

Sciarretta Farms said...

Very interesting! I have a question: I have VERY dry skin, only kept at bay by using handmade soap and lotion. I also get electric shocks when touching metal, to an unusual degree (we're talking blue flames), especially in the winter time when my skin is even drier. Is there a correlation between the two?

goodgirl said...

Interesting posting! I didn't get a chance to thoroughly read all the publications but from my and my family's and friends' experience I definitey disagree with soap being bad for your skin.

Take my mom. She's had problems with dry skin on her hands for years, especially during winter when her finger tips even craked and bled sometimes. For almost 5 years she has been using my handcrafted soap. And since then, no bleeding hands anymore.

Same with the eczema my cousin's hubby has been fighting against. He tried cheap and expensive shower gels, from supermarket to pharmacy products. Nothing helped, he had all the same itchy, flaky skin. Well, I recommended my soap, just to give it a try. And he's only had problems with his skin when he switched back to shower gel in an emergency "oh-no-i-ran-out-of-soap"...

Coincidence? Good luck? Wouldn't think so.

In my opinion, removing the skin fat (not sure about the proper English term) which is exactly what surfactants in shower gels and body washes do, is worse than a short pH shift.

I would also like to point out that the pH drop Lambers et al. (all working at SaraLee) mention in their paper is marginal at best. The standard deviation is too high, and they don't give a P-value for the whole group, just subgroups. Look at their other experiments, their error bars are horrible.

As far as I see, this does look a bit like a "that's how I want it to be" instead of an "this is how it is".

And then they "estimate" what they call a natural skin pH?! Later in the discussion, they repeatedly talk about they have demonstrated this pH value which they just said is an estimation? I cannot take this seriously. This is no good scientific research.

Sorry about ranting but publications like this one make me angry just like you and this infamouse cosmetics database (I forgot the name of ot ; ).

goodgirl said...

Aaaah, I just noticed some typos and grammar mistakes, sorry about that. Too much ranting about bad science ;).

Jo said...

I knew it, tap water is not my skins friend. So with ur informative post I am right back at the beginning. I actually bought some Micellar cleansing water 2day. With a view 2 limit the amount of tap water on my face. If I can tolerate it, more the eek factor of not actually washing face, then will look into duplicating. Or rather asking you....... I digress. I look forward 2 ur post 2morrow.
How did the cake decorating go?

Briny Bar Soap said...

Looking forward to tomorrow's post!

Jo said...

Hi goodgirl, I have 2 agree with u in regards 2 the research study above. We all would love 2 see gold standard randomised controlled trails. But they are time and cash expensive, so 2 enable potential backers 2 b interested then studies like these r put out there. So what they "discover" can b taken 2 fund further studies.
. As 4 the soap issue it really is horses 4 courses. There are so many variables in which chemical combination suits one person than another. Environment, diet, race, body chemistry we could go on. I suffer from a reactive skin condition, my mum makes amazing soaps, I can't use them here in London but lovely holidays in the Caribbean mean I can use her fantastic supafatted soaps n my skin loves it. Is it the water, the climate, the fresh fresh foods, the sunshine attitude or the local rum? It's all of it. Until I can up sticks n move my family, I have 2 limit the variables that have an impact on my skin and using soap, even soap my baby can use is one of them. However the fact that ur lovely soap actively helps those closest 2 you is great, no denying it. But one size doesn't fit all and this study might helps 2 open up the options 4 people who do not fit in the majority slot.
Wow that is ny rant 4 this evening.
Peace. Jo x

Sânziene şi Mătrăgună said...

Hi Susan!

I hope this is the right place to ask this question... so here it is:

HOW DO WE CALCULATE THE pH OF A FORMULA?

for example, I want to make a 10% lactic acid body lotion. I want it to have a pH around 4. I write down now a "dummy" formula:

10% lactic acid
10% aloe vera juice
5% BTMS-50
2% panthenol
5% caprylic / capric glycerides
5% IPM
2% hydrolized wheat protein
2% hydrolized oats protein
0,5% liquid germall plus
0,5% allantoin
up to 100% - water.

After I make the lotion, I am checking the pH and , if too acidic - I have a NaOH solution to drop it down and, if too alkaline, I can use a citric acid solution to lower it.

BUT in this case, my entire % will be messed up! I will no longer have 10% lactic acid, but something slighter lower. How do I calculate on paper what will be the pH of my cream, and how so I chose how much NaOH or citric acid I should add , so that overall I am at 100%?

so far, I've been pretty average, adding the pH adjusters at the end of the process and NOT compensating for the evaporated water during the cool down phase.

but... isn't there a more elegant way to calculate this on paper, so that when we are making our formula we will know for sure the pH without using pH meters/strips and adjusting the pH?


tough question, I guess... I would really LOVE to see a post on this - how to calculate the pH of a product and how will 1g of lactic acid change the pH of a 100g product of pH 5, for example :)

Susan Barclay-Nichols said...

Hi Sanziene. It's a great question, but there's no easy answer to it, and it's way more complicated than just measuring pH with a meter!

Here are a few sites that explain the concept nicely. The only thing I can suggest is to get a pH meter as figuring this out is pretty much impossible. The problem we have is that nothing we use is considered a strong acid or strong base - except for lye - so we would have to figure out the pH of each ingredient to get the concentration of each acid and base. The only way to truly figure it out is to do it experimentally, which is to say that we would use a pH meter.

My favourite one: ChemGuide

Calculating pH (Purdue University)