Can glycerin/humectant dry your skin and hair?

gilbegilbe Member
Hello everyone :)  

Can someone help me with this question please? I've read the following:

"Humectants attract moisture from their environment, which can be the outside air or the underlying layers of your skin. If you are in a humid environment, humectant ingredients will pull in moisture from the air and therefore help your skin to stay hydrated. If you are in a dry climate, on the other hand, humectants can cause your skin to become dehydrated by pulling moisture up from deeper layers and onto the surface, where they can evaporate into the air. For this reason, it is best to combine humectant ingredients with occlusives."

Would you agree with this? Therefore, can glycerin/humectant dry skin or hair? Can a chemist/specialist answer to this question? 

Thank you!

Comments

  • PharmaPharma Member, Pharmacist
    Many humectants are more or less skin penetrable and therefore don't just sit on your skin.
    Hair is a different story: It contains as much moisture as relative humidity allows it to. Adding a humectant on it will result in better moisture binding. But yes, most of it will be superficial.
    Gotta run, sorry...
  • gilbe said:
    Hello everyone :)  

    Can someone help me with this question please? I've read the following:

    "Humectants attract moisture from their environment, which can be the outside air or the underlying layers of your skin. If you are in a humid environment, humectant ingredients will pull in moisture from the air and therefore help your skin to stay hydrated. If you are in a dry climate, on the other hand, humectants can cause your skin to become dehydrated by pulling moisture up from deeper layers and onto the surface, where they can evaporate into the air. For this reason, it is best to combine humectant ingredients with occlusives."

    Would you agree with this? Therefore, can glycerin/humectant dry skin or hair? Can a chemist/specialist answer to this question? 

    Thank you!

    Yes that is how humectants work, but I would argue they have a very different effect in skin to hair.

    Skin: The primary mechanism of a humectant is pulling water outward from the lower layers of the skin, but if you consider that it dehydrates the lower layers, then they will pull more water from even deeper by osmosis. Therefore the skin will just pull more water from the blood as it does usually when water evaporates from the skin as sweat - so on a very small scale you might need to drink a bit more to replace it. The act of including an occlusive agent provides a physical barrier to prevent water evaporating. Vaseline is a good example. I would suggest that occlusives work alongside the glycerin to retain moisture in the skin, rather than being required to counteract any side-effects.

    Hair: Contrary to consumer belief, "moisture" (=water) in hair is negative. Consumers would label hair which feels soft, smooth and healthy to the touch as being "moisturised", when actually it is the opposite - it contains an appropriate level of lipids, particularly on the surface (conditioning agents), which smooth the surface, and is very low in water content. When hair is wet it is plasticised, allowing it to stretch further than it should do, and increasing breakage of bonds in the parts of the structure that are not plasticised. This is why it is inadvisable to brush/comb the hair when it is wet, because the hairs will stretch more than they should be able to and are therefore more prone to breakage. Frizzy hair on a rainy day is caused by moisture - in humid conditions the hair takes on more water and is plasticised so it bends whichever way it likes, which is usually undesirable especially if the wearer has straightened or styled the hair. 
    Using a humectant in hair products will probably make it feel what the consumer perceives as "drier", as it attracts water, plasticising the hair and increasing frizz and decreasing combability.
    I think the only reasons they are included in hair products is to aid dispersion of conditioning agents (such as guars and thickeners) and perhaps to improve manageability during styling, but they don't serve much purpose once the hair has dried.

    To conclude: No, I don't believe humectants are drying to skin, but I do believe they are drying to hair which is reflected in their concentrations at perhaps 1-10% in skin products but <1% in hair products.
  • EVchemEVchem Member
    Great question and answers so far! I want to learn more about hair because it really has different needs than skin even though consumers may use the same terms (like 'moisturized'). @klangridge do you have any resources on hair care formulating you recommend?
  • @EVchem Unfortunately most of my formulation knowledge has come from my degree, been passed on from colleagues or is from paid courses or conferences. I would recommend looking up TRI Princeton's courses if you have financial backing; their course covering Fundamentals of Hair Science is very useful. You may also be able to join a society or group in your country which supports education and distributes the latest discoveries in cosmetic science - I am a member of the Society of Cosmetic Scientists in the UK and receive copies of the International Journal of Cosmetic Science which I find very useful, and they also run a distance learning course.

    Otherwise, I find the occasional article from sources such as Cosmetics Business, Cosmetics & Toiletries, Personal Care Magazine etc are of use. If you sign up to updates then most of their articles and related magazines such as SPC are free to access. You can also gain a fair amount by looking at guide formulations provided by raw material suppliers - I often use these as a basis when working out what concentrations to use materials at in various formulations, especially when I come across something unfamiliar.

    Here's an example article I found which backs up my claims on moisture in hair (you may need to have an account to access the full article):
    https://www.cosmeticsandtoiletries.com/research/chemistry/161976615.html

  • @klangridge I read this white paper, which is most likely biased as it's produced by a manufacturer https://www.kuraray.eu/fileadmin/product_ranges/isopentyldio/downloads/IPD_in_Hair_care_final_end.pdf

    They had this catchy picture of hair soaked in 5% isopentyldiol and sorbitol


    I wonder if it's a temporary effect..
  • PharmaPharma Member, Pharmacist
    I think I read this paper (or a similar one with that 5% & 5%)... weird enough that IIRC only the mix performed outstanding and sorbitol alone had some effect whilst isopentyldiol alone wasn't mentioned. It probably didn't do much and was hence suppressed from publication.
    Regarding hair 'health', don't look at the pattern (colouring) but the edge of the hair (shape) to see whether there are 'scales' pointing out like an old pine cone or if it's all straight and smooth like a copper wire. Trying to ignore background (which is more disturbing in the untreated hair, especially on the right half) and zooming in, I can't see much of a difference.
    In the treated hair, the white specks may simply be invisible because they are filled with sticky liquid with a similar 'optics' under an electron microscope. An educated guess would be that sorbitol shows that masking effect but since it's only liquid if water is present (which may not be enough if used pure), the effect of the mixture (sorbitol dissolved in isopentyldiol) looks more pronounced. But that's only a guess, I'm not versed in electron microscopy.
  • @ngarayeva001 Interesting paper. I don't like the way it's written because there's a lot of information omitted; simple things like humidity and temperature of drying conditions, and length of drying time.

    I agree - the labelling of the SEM image does not state any test conditions! Even if the treated hair has been allowed to dry, considering both images are at the same magnification yet are different diameters, it could be a completely different hair type, or they could have simply chosen a hair which was less damaged from the selection that were treated.

    The breakage experiment was conducted on dry hair, and we don't know in what environmental conditions - the % RH could have been very low to stop moisture absorption, in which case it could have been the effect of applying ethanol which produced the positive result rather than the IPD.
  • @klangridge I try to be sceptical of the papers written by manufacturers. Let's start from the fact that 5% of IPD and 5% Sorbitol make a rather sticky solution. Nevertheless, sometimes I fall for "shiny objects" such as this paper and give it a go (that's why I know it's sticky):)
    Your explanation about moisture in the hair makes a lot of sense and is very useful, thank you for it. 
  • PharmaPharma Member, Pharmacist
    ...sometimes I fall for "shiny objects"... 
    That's why I organised some IPD... tried a wee bit but wasn't impressed. I kinda expected pink glitter, rainbows, and unicorn farts shooting out of the bottle but my first impression is that of propylene glycol. I should do some more trials but IPD rapidly dropped down the priority ladder after that.
  • @Pharma, I  didn’t notice much difference with propylene glycol either  :( the manufacturer’s materials promised it dissolves salicylic acid better than PG. Same thing but costs more.. I will obviously give it another go.
  • I have read tons of articles....regarding glycerin, and as a result my first product (lotion) did not include it (and it was not missed).  As I am working on the next two releases...I found this study VERY interesting....just looking at glycerin, which was not the topic of the study.  I like studies like this....where the (glycerin) candidate is just a participant...and not being promoted...or discriminated against....Therefore you can probably accept the result without bias.

    https://www.floratech.com/PDFs/ClaimSheets/CS15-071.pdf

    It appears as though.....draw your own conclusion... :) 
  • gilbegilbe Member
    Hello everyone :)

    Thank you so much for your replies! Very useful indeed. Thank you again  :)


  • PerryPerry Administrator, Professional Chemist
    edited May 13
    @Graillotion - in their "study" they use 0.3% glycerin and it is compared to materials like Butylene Glycol at 2%. This is not a reasonable comparison.  Also, their data makes no sense when they include Glycerin plus their material and get a multiple increase in moisturizing. Add to that it was a corneometer study (never very accurate) and it conflicts with previous industry findings, I wouldn't put much faith in their findings.

    In my opinion, Glycerin is generally the best humectant to use in a formula. From a cost / effectiveness standpoint, it can't be beat.  I'd be interested in seeing data that demonstrates I'm wrong.

    See this discussion about glycerin vs hyaulronic acid  


  • @Perry, what is your opinion about sodium lactate? I find it one of the best because it's more hygroscopic than glycerin and not sticky. It has one downside, being a salt, it breaks the gel network (for rheology modifiers like carbomers). I have been exploring urea recently, also like it, but it's a tricky material..
    Between glycerin and butylene glycol I would choose butylene glycol.
  • PharmaPharma Member, Pharmacist
    Does anyone have experience with hydroxyethyl urea? It's said to be more stable and allegedly even more hydrating than urea...
Sign In or Register to comment.