pH of soaps and creams

The outer layer of hair, the cuticle, is a single cell thick layer of hair cells that overlay each other like roof tiles. This layer is responsible for most of a hair's strength. Healthy hair is as strong as copper wire of the same thickness. Hair can stretch about 20% of its length when dry, and 50% of its length when wet. In healthy hair, the outer layer is water resistant. All of this makes it difficult to cut healthy hair.

The inner layers of hair will absorb water. If they do, they'll expand and separate the individual cuticles, like the opening of a flower bud, making it easier to cut through the hair. The easiest way to do this is to (temporarily) "damage" the outer layer by raising its pH (above 7). Most shaving soaps and creams are already alkaline (pH above 7).

The following table lists the pH of a few shaving products. These are crude, one-time measurements, so they shouldn't be relied on for accuracy. They're make by color matching with universal indicator paper. For example, baking soda is knows to have a pH of 8.2, but I can't extrapolate the color exactly, so I call it 8.5 because it looks to be somewhere between 8 and 9. Also note that while pH shows the relative level of alkaline vs acid, it doesn't indicate the actual quantity of alkaline substances in the product, and that's also important.

6.5 My tap water
9.5 Tabac soap
8.0 Art of Shaving soap (unscented)
8.5 Penhaligon's (Blenheim Bouquet) soap
9.0 Mitchell's Wool Fat soap
8.0 Floris soap
9.0 Czech & Speake (Oxford & Cambridge) soap
9.0 Prarie Creations (chocolate dreams) soap
8.0 C&E Nomad soap
8.5 Williams mug soap
9.0 Mama Bear (British leather) soap
9.5 TOBS (sandalwood) cream
8.5 Trumper's (coconut) cream
8.0 Speick cream
9.5 Proraso (ultra sensitive-green tea and aloe) soap
8.5 Pre de Provence soap

2.5 styptic pencil
5.0 alum block
8.5 baking soda

Someone's been busy with the litmus paper! A fine source of info. I was curious about this but never got around to testing it. Thank you!!!!

very interesting, mate

SiBurning said:

6.5 My tap water
9.5 Tabac soap
8.0 Art of Shaving soap (unscented)
8.5 Penhaligon's (Blenheim Bouquet) soap
9.0 Mitchell's Wool Fat soap
8.0 Floris soap
9.0 Czech & Speake (Oxford & Cambridge) soap
9.0 Prarie Creations (chocolate dreams) soap
8.0 C&E Nomad soap
8.5 Williams mug soap
9.0 Mama Bear (British leather) soap
9.5 TOBS (sandalwood) cream
8.5 Trumper's (coconut) cream
8.0 Speick cream
2.5 styptic pencil
5.0 alum block
8.5 baking soda

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Cool! I would have thought tallow soaps to have the highest pH levels, but clearly that's not always the case. Thanks for posting.

This is interesting! Kinda makes sense I guess too. Good on ya mate!

Very cool. I would love to know the pH of Gold-Dachs, which is known to have a higher pH and many shavers find very irritating to the skin.

beginish said:

Very cool. I would love to know the pH of Gold-Dachs, which is known to have a higher pH and many shavers find very irritating to the skin.

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If you want me to do it, you'll have to send me a sample. (PM me) Here's what I have http://wiki.badgerandblade.com/index.php/User:SiBurning. If I ever get really bored I'll do some concentration tests (titrations).

thanks so much for doing this awesome experiment. I knew there was a more technical reason why I loved TABAC and TOBS LOL!

Hooray for SCIENCE! Nicely done, thank you for the data

Re-posting in descending order of pH level (just cause it's easier for me to read that way) :

9.5 Tabac soap
9.5 TOBS (sandalwood) cream
9.5 Proraso (ultra sensitive-green tea and aloe) soap

9.0 Mitchell's Wool Fat soap
9.0 Czech & Speake (Oxford & Cambridge) soap
9.0 Prarie Creations (chocolate dreams) soap
9.0 Mama Bear (British leather) soap

8.5 baking soda
8.5 Pre de Provence soap
8.5 Penhaligon's (Blenheim Bouquet) soap
8.5 Williams mug soap
8.5 Trumper's (coconut) cream

8.0 Art of Shaving soap (unscented)
8.0 Floris soap
8.0 C&E Nomad soap
8.0 Speick cream

6.5 SiBurning's tap water
5.0 alum block
2.5 styptic pencil

So it looks like a Superlather of Tabac+ToBS Sandalwood would pretty much just melt the hair off your face!

Very nice job Steve!

Do you think the mechanism that links higher pH to ease of cutting hair involves the lower concentration of hydrogen bonding within the hair molecules?

Miles said:

Do you think the mechanism that links higher pH to ease of cutting hair involves the lower concentration of hydrogen bonding within the hair molecules?

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Huh?

I'm no chemist. Just a dude with a $1.19 jar of indicator paper.

Two things that make shaving easier are to spread the outer layer so that the blade can get in between the harder outer cells, and hydrating the (outer section of the) inner part of the hair to swell it and make it softer. I've seen this in several books online.

There's another thread about keratin bonds and how pH, salt bonds, and even water affect it: Keep it Simple and Smooth - The Chemistry, Physics, and Science Behind Shaving. I actually posted that thread as my favorite in the carnival because it's so odd and quirky. But I have no idea what actually causes the cells to open and expose the inner layers. I did verify from several books and research papers online that a high pH will do this. I have no idea why it happens, or what a keratin bond is, other than keratin is a protein, and people or proteins both tend to stick tightly to their own kind until something agitates them.

I'll throw out some other factors, but keep in mind these are for hair on the head, which has been exposed much longer. There really isn't much time to damage beard hair when you shave every day.

Most kinds of damage do the same thing--break the hard protective outer layer, exposing the inner part of the hair. I was reading this from a book on hair conditioners. Heat is a big factor, but it seems to require a lot of heat, like the kind you get from a hot roller that sits too long. Well, that's temperature, not heat, so a hair dryer can still do permanent damage. Friction is the biggest thing that damages the outer layer, and can damage the layer just by the hairs rubbing together when we brush. This kind of supports the experience of people that do an exfoliating wash or rub the brush around vigorously.

One odd thing that you can verify yourself is that hair has a grain, so there's twice as much friction rubbing towards the root than away. Skin apparently also has a grain. Don't know how to work that into a shaving routine.

And, by the way, this experiment was inspired by the carnival.

Miles said:

Do you think the mechanism that links higher pH to ease of cutting hair involves the lower concentration of hydrogen bonding within the hair molecules?

Click to expand...

After a little more research...

The heachache-lite version is that lye breaks fat into soap, and also breaks up the outer layer of hair. Fat and hair both dislike water, but lye is like the mean baby sitter that makes them tolerate water. So the lye lets water get inside the hair and that makes the hair easier to cut. Shaving soaps and creams both have a mean baby sitter in them. So just go wash your face, or let the shaving cream sit for a while, but don't use a pH balanced shaving cream unless you absolutely have to.

[MIGRANE_HEADACHE_WARNING]
Hair is mostly made from keratin proteins that has a lot of disulfide from the amino acid cysteine. The disuplhide bonds are responsible for arranging the protein to have a hydrophobic (water repelling) part. This hydrophobic bond is the important thing to break in order to hydrate and swell the hair making it easier to cut. (I'm guessing the the hydroxide is enough to unfold the protein, which might be enough to swell the cells.) Water takes care of the rest, and will break the relevant hydrogen bonds all by itself. (Although I wonder if that's also pH dependent.) We're not trying to tear the proteins apart, so we don't care about the hydrogen bonds that hold the protein together. We're just trying to wet the hair by getting water into the cells, probably by plain old osmosis.

The best I can make of the chemistry is that a disulphide bond is formed by oxidation via hydrogen. So the reverse is to use hydroxide, which is a natural base. There's a lot more to it that I don't understand, parts of which are hinted at in Wikipedia's article on ammonium thioglycolate, used in perming hair. In particular, it looks like most anything that breaks disulphide bonds is pH dependent. There are articles online that show other ways to break the bonds, but those are also pH dependent. This leads me to think it's not the pH itself that breaks the bonds, but the presence of hydroxide in the soap (from lye), and that the pH only makes the reaction proceed easier and faster. Of course, it's kind of quibbling to argue pH vs. OH-. At least for most things we'd put on our face for shaving. Ammonia works even better, but who's gonna use that? And it leads me to wonder whether baking soda would do the job at all. (Or does the acid component reverse the reaction?)

Maybe someone more familiar with redox potentials and dihedral angles can fill in the gaps. I forgot most of it from chemistry 101, but remember enough to know I won't be able to get the right answer. There's too many factors, and I never went beyond chemistry 101 except for some electroplating and etching as a hobbyist.
[/MIGRANE_HEADACHE_WARNING]

[ASPIRIN_HEADACHE_WARNING]
Keep in mind that the whole point of all this is to physically open the hard outer layer (to at least temporarily damage the protective layer) so the blade can catch the softer internal parts, and also to allow water into the hair because that softens the cells. Friction actually enters into this because the blade literally catches on the frayed edges and slips underneath, just as if roof shingles got a bit bent out of shape.

The other thing to consider is that these hair cells have a coating of fatty acids that repel water.

By the way, my original post said that the outer layer is responsible for most of a hair's strength. I don't think that's quite true, and to the extent it is, it's only true going across the hair. The inner layers are responsible for it's strength down the length, which is what matters when you stretch it.
[/ASPIRIN_HEADACHE_WARNING]

SiBurning said:

The outer layer of hair, the cuticle, is a single cell thick layer of hair cells that overlay each other like roof tiles. This layer is responsible for most of a hair's strength. Healthy hair is as strong as copper wire of the same thickness. Hair can stretch about 20% of its length when dry, and 50% of its length when wet. In healthy hair, the outer layer is water resistant. All of this makes it difficult to cut healthy hair.

The inner layers of hair will absorb water. If they do, they'll expand and separate the individual cuticles, like the opening of a flower bud, making it easier to cut through the hair. The easiest way to do this is to (temporarily) "damage" the outer layer by raising its pH (above 7). Most shaving soaps and creams are already alkaline (pH above 7).

The following table lists the pH of a few shaving products. These are crude, one-time measurements, so they shouldn't be relied on for accuracy. They're make by color matching with universal indicator paper. For example, baking soda is knows to have a pH of 8.2, but I can't extrapolate the color exactly, so I call it 8.5 because it looks to be somewhere between 8 and 9. Also note that while pH shows the relative level of alkaline vs acid, it doesn't indicate the actual quantity of alkaline substances in the product, and that's also important.

6.5 My tap water
9.5 Tabac soap
8.0 Art of Shaving soap (unscented)
8.5 Penhaligon's (Blenheim Bouquet) soap
9.0 Mitchell's Wool Fat soap
8.0 Floris soap
9.0 Czech & Speake (Oxford & Cambridge) soap
9.0 Prarie Creations (chocolate dreams) soap
8.0 C&E Nomad soap
8.5 Williams mug soap
9.0 Mama Bear (British leather) soap
9.5 TOBS (sandalwood) cream
8.5 Trumper's (coconut) cream
8.0 Speick cream
2.5 styptic pencil
5.0 alum block
8.5 baking soda

Click to expand...

Wow - tough water there - I thought most water was PH 7.

I guess that explains why I get such a good shave with TOBS sandalwood.

I am a chemist - a biochemist (by training if not profession) and whilst I don't wish to poo-poo your comments some of it seems unlikely to me. I haven't actually done any research on this so I can't quote figures but anyway:

Lye (sodium hydroxide) does indeed convert fat (either fatty acids or glycerides) into sodium salts however I find it unlikely that a pH of the level you're discussing would be able to break amide bonds in proteins such as keratin or indeed break disulphide bond which in any case are usually separated by adding HCl (low pH not high).

Disulphide bonds are not hydrophobic in any normal sense I'm guessing that the material you're paraphrasing says these bonds hold keratin molecules in a particular shape whereby areas which contain mostly hydrophobic side chain amino acids (eg tryptophan) are presented to the outside. A high pH, even if not particularly high, could easily cause minor changes in the conformation of a protein by disrupting hydrogen bonds which are responsible for most of the shape of a protein or by ionizing (or de-ionizing) side chains with pK values in the 7-8 range (or thereabouts).

<i>"Fat and hair both dislike water, but lye is like the mean baby sitter that makes them tolerate water."</i>

The first part is right the second is not - lye converts fat into another substance (soap) it does not then need to be present to 'baby sit' for soap to have it's effect.

<i>"I'm guessing the the hydroxide is enough to unfold the protein, which might be enough to swell the cells.) Water takes care of the rest, and will break the relevant hydrogen bonds all by itself."</i>

I doubt this is correct, water alone probably would not disrupt (any relevant) hydrogen bonds sufficiently to have the effect you're talking about. Yes hydroxide ions (ie high pH) probably would cause at least partial unfolding of a protein - that's almost what you said but I think you got lost a bit.

<i>"disulphide bond is formed by oxidation via hydrogen"</i>

I don't mean to be rude but that's . . . we'll . . . profoundly wrong, for a start hydrogen is a reducing agent (the complete opposite of an oxidizing agent) you cannot (in any but the most extreme situation) oxidize something with hydrogen. Disulphide bond formation is a form of oxidation in a technical sense in as much as you're removing hydrogen and that's the reverse of reduction (opposite of reduction = oxidation).

<i>"This leads me to think it's not the pH itself that breaks the bonds"</i>

No, disulphide bonds are attacked by nucleophiles (generally things with negative charges or neutral molecules with a relatively negative 'part'), OH- is a nucleophile though as I said before I doubt it would be able to break up these bonds significantly at the pHs were discussing.

<i>"And it leads me to wonder whether baking soda would do the job at all. (Or does the acid component reverse the reaction?)"</i>

There is no acid component in baking soda but carbonate ions wouldn't break disulphide bonds (I don't think).


<i>"Keep in mind that the whole point of all this is to physically open the hard outer layer . . . and also to allow water into the hair because that softens the cells."</i>

This is more to the point and I think the key to all this. Soap has a detergent effect making normally hydrophobic materials more miscible with polar solvents like water.

Please bear in mind that (as I said earlier) I haven't researched any of this so my comments just reflect my immediate reaction, I've tried to make it clear where I'm fairly sure of my ground and where I'm mostly guessing but in any case none of this should be taken as gospel.

And, of course, even water at a pH of 7 is alkaline relative to skin and hair's average pH of 5.5 to 6.

In broad strokes from barber school: liquid bases open the hair's cuticle and allow the middle layer of the hair - the cortex - to absorb water (and other chemicals). This softens the hair and causes it to swell. Lucky for us that a good soap or cream also offers lubrication and cushion. Quality lather is a wonderful thing.

Acids close the hair's cuticle making the hair smoother, harder and shinier. When you wash your hair the shampoo is base. The conditioner is acidic. I can never understand assertions that putting hair conditioner on a beard as prep gives a better shave.

The hydrogen cross bonds in hair are easily broken by heat, moisture, or a combination of both. Fortunately, these bonds reform as easily as they're broken. My mother used to put rollers into wet hair, let it dry and the curl stayed until the next time the hair got wet. My ex-wife could either curl or straighten her hair when it was dry depending on her choice of heated appliance. Heat the hair, form it the way you want it, let it cool and it stays that way until the next time the hair gets wet or re-set again with an iron.

I'll add that TOBS Lavender and Almond and JM Frasers all came in at 9,5 when I looked at them. Thank you for taking the time to test all that stuff and share it. This is great information. We had a lot of discussion at school about whether sensitive skin was aggravated by pH, scent additives or a combination of both. I believe your results confirm my belief that it's scent, not pH, that usually causes problems in shave products. Of course, having said that, I still recommend either Dickinson's Witch Hazel or, preferably, a moderately priced alcohol based toner like Neutrogena Pore Refining as an aftershave splash in order to bring the skin's pH back down to normal.

Regards,

Les

trewornan said:

I am a chemist - a biochemist (by training if not profession) and whilst I don't wish to poo-poo your comments some of it seems unlikely to me. I haven't actually done any research on this so I can't quote figures but anyway:

Click to expand...

Thanks for taking the time to clarify. Your response are completely in line with what I read. Maybe I'd say things better if I had more of a clue, which is why I asked for help. Yes, I get more than a bit lost in this.

I hate to break this up piece by piece, but it seems the best way to clarify. Some of it is kind of off topic or irrelevant, though.

Lye (sodium hydroxide) does indeed convert fat (either fatty acids or glycerides) into sodium salts however I find it unlikely that a pH of the level you're discussing would be able to break amide bonds in proteins such as keratin or indeed break disulphide bond which in any case are usually separated by adding HCl (low pH not high).

Disulphide bonds are not hydrophobic in any normal sense I'm guessing that the material you're paraphrasing says these bonds hold keratin molecules in a particular shape whereby areas which contain mostly hydrophobic side chain amino acids (eg tryptophan) are presented to the outside. A high pH, even if not particularly high, could easily cause minor changes in the conformation of a protein by disrupting hydrogen bonds which are responsible for most of the shape of a protein or by ionizing (or de-ionizing) side chains with pK values in the 7-8 range (or thereabouts).

Click to expand...

Yes, it seems to be about protein unfolding.

What I remember reading is the disulphide bonds hold the protein in a certain shape, and cause the hydrophobic or hydrophilic parts to bunch up together in the center, so it was the disulphide bonds that had to be broken.

It wasn't clear whether the interior was hydrophillic or hydrophobic. It seemed like the interior cluster was hydrophyllic, in which case it would be the blob that prevents water from penetrating further.

I may be confusing things here because some of the information was referring to damage in general, others were about hair styling techniques such as perms and dying. The information on shaving is very sparse.

"Fat and hair both dislike water, but lye is like the mean baby sitter that makes them tolerate water."

The first part is right the second is not - lye converts fat into another substance (soap) it does not then need to be present to 'baby sit' for soap to have it's effect.

Click to expand...

It's a bad analogy. If the analogy falls apart so bad that it suggests bad chemistry, that's my bad.

"I'm guessing the the hydroxide is enough to unfold the protein, which might be enough to swell the cells.) Water takes care of the rest, and will break the relevant hydrogen bonds all by itself."

I doubt this is correct, water alone probably would not disrupt (any relevant) hydrogen bonds sufficiently to have the effect you're talking about. Yes hydroxide ions (ie high pH) probably would cause at least partial unfolding of a protein - that's almost what you said but I think you got lost a bit.

Click to expand...

I'm clearly confused here because I don't know what else needs to be done after the protein unfolds. Perhaps "the rest" is just absorption into the cells. There was a strong suggestion that something more complicated was invovled.

I think you hit it below when you talk about soap.

"disulphide bond is formed by oxidation via hydrogen"

I don't mean to be rude but that's . . . we'll . . . profoundly wrong, for a start hydrogen is a reducing agent (the complete opposite of an oxidizing agent) you cannot (in any but the most extreme situation) oxidize something with hydrogen. Disulphide bond formation is a form of oxidation in a technical sense in as much as you're removing hydrogen and that's the reverse of reduction (opposite of reduction = oxidation).

Click to expand...

Guilty as charged!

Kind of off topic, but...

I plead for leniency. I said this wrong, but I've also always looked at this backward anyway. Maybe in a strange way, two wrongs make a right.

In my defense, you can't have oxidation without reduction. It depends which side you look at. I do some electro-plating and etching, and am typically more focused on the bath, not the metal, at least in terms of the chemistry. In the bath or solution, you get reduction. The oxidizer itself, typically oxygen or chlorine, often comes out of solution as a gas. The reduction is typically done by hydrogen. In terms of maintaining the bath, the effect is that hydrogen gets oxidized.

I admit it's wrong to talk about an oxidation reaction like this, since I'm really talking about a secondary reaction further away. Even so, the way I said it is wrong, even to my backward way of thinking.

"This leads me to think it's not the pH itself that breaks the bonds"

No, disulphide bonds are attacked by nucleophiles (generally things with negative charges or neutral molecules with a relatively negative 'part'), OH- is a nucleophile though as I said before I doubt it would be able to break up these bonds significantly at the pHs were discussing.

"And it leads me to wonder whether baking soda would do the job at all. (Or does the acid component reverse the reaction?)"

There is no acid component in baking soda but carbonate ions wouldn't break disulphide bonds (I don't think).

Click to expand...

This part came from reading about other mechanisms that don't involve OH- directly. I forget if it was using some fancy chemicals and catalysts, or if this is from using UV, but I ran across a couple of these mechanisms where the process was faster in a high pH.

The suggestion is there may be other things at work here besides merely the pH. As for baking soda, the other thread talks about baking soda, but, like you, I'm left to question whether it would work, even though a saturated solution has a similar pH to shaving soap. By the way, I was thinking of the carbonic acid.

My takeaway from this is that it could be interesting investigating which substances do a better job at unfolding.

"Keep in mind that the whole point of all this is to physically open the hard outer layer . . . and also to allow water into the hair because that softens the cells."

This is more to the point and I think the key to all this. Soap has a detergent effect making normally hydrophobic materials more miscible with polar solvents like water.

Click to expand...

This might be where "water does the rest". Once the protein is unfolded a little, the soap could bond to the hydrophobic part allowing water to seep in. Perhaps without the soap letting the water in, the unfolded protein would just collapse again.

Please bear in mind that (as I said earlier) I haven't researched any of this so my comments just reflect my immediate reaction, I've tried to make it clear where I'm fairly sure of my ground and where I'm mostly guessing but in any case none of this should be taken as gospel.

Click to expand...

Well, you seem to be spot on as far as I can tell.

Thanks!

Scotchd said:

Wow - tough water there - I thought most water was PH 7.

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From: http://www.water-research.net/ph.htm
The normal range for pH in surfacewater systems is 6.5 to 8.5 and for groundwater systems 6 to 8.5.

The pH of pure water (H20) is 7 at 25oC, but when exposed to the carbon dioxide in the atmosphere this equilibrium results in a pH of approximately 5.2.