Article by: Perry Romanowski

When I first got into the cosmetic industry I worked on hair care products, specifically, shampoos. One of the things that I found fascinating about shampoos was that if you added salt to them they would get thicker. I later found that if you added too much they get thinner. It turns out there is a range of salt concentrations at which a shampoo formula will get thicker or thinner. We call this the Salt Curve and it is an important thing to know because it can help save many production batches.

Salt Curve and Shampoos

To understand why salt affects the viscosity of a shampoo (or body wash) you have to first realize that shampoos are mixtures of surfactants that arrange themselves in tiny structures called micelles. The viscosity of the shampoo solution depends on the size and packing structure of these micelles.

Since shampoos are typically made from anionic surfactants the outer surface has a specific charge density. This will affect the way that the micelles can pack together. A higher charge density will cause the micelles to repel and result in a thinner solution.

The sodium ions from the salt lower the charge density of the micelle surface. This makes them more able to pack closer together and creates a thicker solution. This is why salt thickening is really only affective with anionic-based or anionic/nonionic-based shampoos.

Micelles and salt

While salt can help increase the viscosity of a shampoo system, it works differently in different formulas. Some systems will be highly tolerant of salt while others get thin as water with just a small increase in salt concentration. This is because the size of the micelles is dependent on a number of factors including

  • Concentration of surfactants
  • Type of surfactants
  • Ratio of surfactants
  • Temperature
  • Charge density

The way salt reduces the charge density is that it pushes the dissociation equilibrium of the surfactant to the left. As an example, consider this dissociation equation for Sodium Lauryl Sulfate.

C12SO4Na = C12SO4- + Na+

More sodium ions push the equilibrium to the associated state.

This drops the micelle charge density and the size increases. This in turn causes more micelle agglomeration which can ultimately lead to lammellar structures which can form a gel.

Creating a salt curve

When formulating an anionic cleansing system, it is useful to create a salt curve so when your manufacturing people present you with a product that is too thin, you’ll know exactly how much salt they should add to get the right viscosity. Here’s how you do it.

1. Make a 500 g batch of shampoo (or body wash) and leave out the salt.

2. Split the batch into ten 50g samples.

3. Add salt levels in the following increments. (0.2%, 0.4%, 0.6%, 0.8%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%)

4. Record viscosity & plot viscosity versus concentration.

Most systems should not tolerate much more than 2% salt levels. Based on the results you can refine your salt curve to figure out even tighter % levels.

Each formula type you make should have a salt curve like this so you can tell Production how much they’ll need to add to adjust the viscosity. You might also consider doing the same thing with the fragrance as it can affect the viscosity in a similar way.

Why?

We’ll save that answer for another time.

97 comments

  1. SADDAM

    PERRY SIR PLEASE TELL ME HOW CAN ANALYSIS OF SALT IN THE SOLUTION OF HAND SOAP.

  2. Hina

    Can we replace sodium sulphate with fine rock salt(90-92% NaCl) for detergent powder formulation ? what will be the consequences, kindly explain for better understanding.

    1. Perry Romanowski

      I don’t know. I haven’t made powdered detergents.

  3. Ariram V

    Hello Perry,

    What would be the PH effect on NaCl based thickener in toilet cleaner?

    1. Perry Romanowski

      It can either thicken or thin it. It really depends on the system.

  4. Nk

    Please sir ,
    When is the best time to add propylene glycol in sle,s cdea and capb based liquid detergent. E.g. last or first in water.
    Thanks.

    1. Perry Romanowski

      Probably best to add at the beginning.

  5. birhan

    Hi pery my question is about amount of table salt production of liquid soap from 154g labsa, 25g silicat, 2.2g cmc, 17.3g soda

    1. Perry Romanowski

      I don’t know. You’ll have to do an experiment to find out. Start with 0% and go all the way to 2% until you get the thickness that you want.

  6. Muhammad Din

    Can we add citric acid instead of sodium salt in liquid soap for increasing the viscosity of soap?

    1. Perry Romanowski

      No. It won’t work the same.

  7. bhupesh nanawati

    you forum is very good and knowledgeable i am mfr of hand wash and utansill liquid cleaner
    one product on the base of acid slurry (LAB) nutrilzed with NaOH added urea For Transparancy and Add Global Salt and sale pure THikend Anionic Liquid Wash with BAlanced ph
    second start know sles and common salt problem is that less foming can you help me what chemical i add to improve foam.

    1. Perry Romanowski

      You haven’t provided enough information for me to answer. I would suggest you post your question in our forum with more information about exactly what is in your formula. “Anionic Liquid Wash” is not descriptive enough. http://chemistscorner.com/cosmeticsciencetalk

  8. Priyanka G

    Hi Perry,
    Your article is brilliantly informative! I am working on a soap/detergent formulation and I am told to just add Magnesium and citrate salts for reasons unknown to me! This is messing up my entire formulation in terms of clarity at required pH. I was scouring for information on why to use salts at all and then I found your article. So thank you… Now at least I know!!
    Coming to the problem, I am working on SLES+LAS mixture (7-10% by weight) with a few additives for foam/ fragrance and what not. At my required pH, the formulation is translucent and the moment I add the Mg and Citrate salts, I end up with cloudy white goop. Do you mind answering a few of my queries?
    PS: Don’t worry, I have more chemistry/physics kind of questions and not ‘Could you Please do my work for me” kind. Thanks in any case. I’m not even sure if this thread is still active.

    1. Perry Romanowski

      Hello – I’d suggest you post your question in our forum to get more chemists involved in the answer. http://chemistscorner.com/cosmeticsciencetalk

      To answer your question is not possible with the limited information you provided. I’d need to know what the exact formula you are making.

  9. Sabah Jawad

    I am looking for a Chemist / Company to custom formulate a deodorant roll on solution for our active ingredient 5% Copper Chloride solution pH3.
    Thank you

  10. Cristina

    Viscosity of liquid hand soap
    Hello, I would appreciate your help to improve the viscosity of liquid hand soap. I am new at this and I’m doing my first experiences.
    The formulation is:
    SLES (25%): 30%,
    Cocamidepropyl Betaine: 2%
    Cocamide DEA: 2%
    Glycerine 2%
    SDS 1%
    and EDTA, metyl paraben, fragrance and dye
    The pH range of is from 5.5 to 6
    For the viscosity I use NaCl (after testing different concentrations of NaCl) and in fact I can achieve a good initial viscosity.
    The problem is after about 72 hours (I suppose after the formulation is stabilized), the viscosity decreases substantially.
    What can I do that the viscosity remains stable over time? Should I change something of the formulation? It could be the quality of salt, since I’m currently using table salt?
    Thanks

    1. Perry Romanowski

      I would suggest you run your salt curve analysis after letting the system equilibrate for 72 hours. The other option is to include something like Methylcellulose at around 1%. But you should be able to achieve this thickening with salt and a pH adjustment alone. Remember to check to see if your pH is changing.

    2. frank

      You don’t really have any problem. It could be as a result of some chemical reactions taking place. Contact me and I will solve the problem for YOU at a very cheap rate. They say information is power.+2348094297500

  11. Chrisaredel Dizon

    Thanks for sharing this, It helped me how to thicken my shampoo for my Science Investigatory Project. Only I’m a little bit confused and lost on its measurements. . . What kind of materials are you going to exactly to have the exact measurement? If too much salt or less Salt, would it affect my product?

    1. Perry Romanowski

      The materials you measure are the salt and your formula.

  12. Khalid Rashid

    I am trying to make a liquid diswash detergent for some one.I got success 90/ but same problem faced that viscosity goes down.in my opinion it is occurring due to surfactant heavy water and perfume.

  13. Dana

    Hello,
    First, thank you for posting this helpful article.
    I would be grateful for your opinion, what makes the shampoo – BIG, made by Lush, thick at a very high level of the sea salt, maybe 50 % , and if you think the salt is dissolved or stays in solid form in the formula, and if a solid, undissolved form can be effective in the formula. Here is the link for BIG with ingredients :
    https://uk.lush.com/products/big
    Thanks in advance

    1. Perry Romanowski

      It looks like they use a low level of water so the salt doesn’t dissolve into the formula. The thickness in this case is not from the salt but from the lack of water. It seems like the formula would be pretty irritating to eyes but I don’t know for sure.

  14. Jaideep

    Very nice to join and tobe a part.looking forward.

  15. Aluko afolabi

    Yes use salt,but remove cmc in your formulation

  16. chris

    How do we determine if our system is anionic, cationic or non-ionic? Is it only decided by the surfactants? What if we have both anionic and cationic ingredients?

    1. Perry Romanowski

      Usually, anionic and cationic surfactants are not compatible and they create a precipitate when mixed. You determine whether the system is cationic or anionic based on the surfactants used.

  17. Victoria

    Dear Perry,
    What is the kinetics of viscosity raise of an emulsion with salt?
    Could it take even a few days to stop viscosity increase?
    Thanks in advance and regards.

    1. Perry Romanowski

      That depends on the system. You have to take measurements to find out. Usually salt effects happen very quickly after you add it.

  18. kassahun Yaie

    Dear Sir,
    Actually I am preparing multi purpose liquid detergent and I use ingredients like labsa,sles, STPP, soda ash, caustic soda, fragrance and thickening agent NaCMC but I couldn’t get the desired thickness so if I use salt in the already formulation can it improve the thickness? Thanks!

    1. Perry Romanowski

      Do a salt curve analysis.

  19. Manon

    Hi, and many thanks for your article. I am currently working on a cationic emulsion, where 0.01% NaCl is added to the formula. There is inside in particular colloidal oat flour, and Varisoft (quaternary ammonium cationic surfactant). Formulators told me NaCl is used as a viscosity agent and a stabilizer. But in your article you say NaCl is generally used in anionic emulsion. So what do you think is the role of NaCl in cationic emulsion, and of this very low concentration ? Thank you so much !

    1. Perry Romanowski

      NaCl in this system could be helping to stabilize the emulsion particles. It is true that it is usually used in anionic systems to create a thickening effect but it will also have a stabilizing and potentially thickening effect in cationic systems. It just won’t work in non-ionic systems. It’s also not usually used in cationic formulations because it can interfere with the emulsion creation. Salt works better on micellular systems rather than emulsion systems.

  20. fukru

    what is the relation b/n home made liquid soap and salt?

    1. Perry Romanowski

      That depends on what the composition of your soap is. Do an experiment and find out.

  21. C.S.Rajagopalan

    Dear
    What is the percentage of salt to be added for a body wash containing 24% of Disodium lauryl sulfosuccinate. 2% of SLES and 2% of CAPB to effect ively thicken the final product

  22. Dawood Abdul Wahab Munir

    Hi Perry,
    i have being making body wash with sodium loureth, sodium chloride, glycerine, propylene glycol, water, form booster, eucalyptus oil. but i found out that my soap does not bubbly well when use. How do i make bubble, or am i doing something wrong?

  23. David

    I found this article after trying to make an hydroalcoholic carbomere gel with an extremely high salt content. The idea is to have a gel that holds as much salt as possible. Like Perry said in the article, I found that the salt removed the viscosity altogether. Am I barking up the wrong tree with the carbopol? I am looking for something that leaves very little residue after evaporation, and evaporates quickly. This is whyI was hoping that the carbopol would work. Thanks for any suggestions anyone has!

  24. adib

    I use 20% alfaolefin sodium sulfonate(40%) in my shampoo as primary surfactant. Is it too harsh?

  25. Akpo

    Pls, when is the best time to add the salt to the shampoo formula? is it after adding all the ingridients including fragrance? and at what temperature were it surpose to be added. pls any one with insight help.

    1. Perry Romanowski

      Yes. It’s best to add it as the last ingredient.

    2. vinayaka.y.s

      After adding polymer, along with all ingredients to shampoo batch add NaCl. 30°C or room teperature is prefered.

  26. Nandkumar Sonar

    The information is quite useful

  27. tywo

    thanks all for the wonderful contributions……i also experience similar situations often.
    i work with sls, cdea, nacl and the end result is fantastic but as soon as i add fragrance it becomes watery drastically. as a matter of fact, i thought its due to a particular fragrance until i experiment with 6 different fragrances but are the same, become watery..
    lastly mr perry, keep the good work and more grease to ur elbow. i include stpp in my formulation becos of water hardness what can u say to that?
    you are doing a gr8 work sir, i planned to attend one of ur seminar last yr but was denied travelling visa but hopefully i will take one of ur online course this yr.
    thanks all

    1. abolfazl

      Hi how are you :can you send me a step to step by detailes and grams of ingredients
      and how time must stirre mixer and how and when I must cotrol PH .thanks

  28. FREDDY ROJAS

    I am writing to ask if you teach how to make shampoo formulas and the method to mix every ingredient. I am really interested in this and I there is no any school to teach it. I would be very grateful if you could give me any additional information or suggest me places where I can get some lessons.

    I am looking forward to hearing from you,

    FREDDY ROJAS

  29. C.S.Rajagopalan

    Sir

    I am using Disodium lauryl sulphosuccinate as the primary surfactant (36%) using 1.1 % PEG -150 distearate in my Face wash preparation. I have taken consecutive batches and dont find any problem in my viscosity. One fine day having doing the formulation with the same thickener with the different lot of Dosiu-Lau-sulphosuccinate I found the final viscosity dropped down drastically. I knew the problem is due to the sulphosuccinate and this has happened. If such things are happening intermittently what shall we do because we cannot alter the formulation again and again. Please advice…

    1. Perry Romanowski

      Find a better, more reliable supply of Disodium Lauryl Sulphosuccinate.

    2. sulastomo

      usually if using sulphosuccinate surfactant it’s difficult to thickening, my opinion you can
      using polymer (acrylate polymer or crosspolymer or cocamide (MEA, MIPA or DEA).
      But some time polymer can cause sticky or stretching feel and cocamide type can cause clean and dry so you have to consider about moisture agent.

    3. C.S.Rajagopalan

      Sir

      Why all the face wash preparations are usually slippery in feel after application? How to avoid this slippery feel while making these formulation. Will adding sodium chloride can over come this matter.

      1. Perry Romanowski

        This has to do with the surfactant you are using. If it binds to the skin too well it can feel slippery. No, sodium chloride will not over come this matter. Try lowering the level of surfactant or use a different surfactant.

        1. C.S.Rajagopalan

          Thanks sir

          Can you suggest which surfactant groups we can use for Face wash preparations?. We are interested only with sulphate free surfactant systems

          1. C.S.Rajagopalan

            Mr.Perry

            It is taking too much time for getting registered in that web address you have mentioned. Kindly suggest how to proceed further to register myself and also for following my doubts further…

          2. C.S.Rajagopalan

            Dear Sir

            What makes the difference when we add Capric Triglyceride in Body wash and Face wash preparations?. How the end product looks?

  30. zahra

    I already made my shampoo, just when I add fragrance , viscosity drop too much. I try with different range, different types, and Solvent?

    1. Perry Romanowski

      Well, you need to use a different fragrance or less of it.

    2. Azeem

      Please check the pH of Fragrance and the solution you added for. Also check the inoic nature of surfactant you use with the ionic nature of Fragrance.

    3. sulastomo

      some time fragrance contain solvent to soluble fragrance on surfactant like PEG-40 hydrogenated castrol oil or polysorbate-20 (example and many more). i prefer to add polymer or co-surfactant to reduce effect of fragrance.

  31. Eric Karanja

    Hallo

    Kindly advise me on the eco-friendly ingridient to use when making a toilet bowl cleaner liquid,

    Inform me on the acid to use, essential oil, enzymes, antispetic, stabilzers n sufracant to use.

    Regards

    1. Brian

      Pliz, help us on issue about toilet bowl cleaner

  32. Nihal

    Hello Perry!

    Your book ‘conditioning agents’ is amazing! I’m a student studying Cosmetic Science and am doing a little research on viscosity and stability. My project is on hair shampoos in which we used sodium chloride for a thickener due to the anionic sodium laureth sulfate. We take measurements every week on viscosity in which it varies (decreases or increases?) I am trying to understand on why does this happen? 🙁

    Thank you for your time!

    Nihal

    1. Perry Romanowski

      Thanks for the kind words. There shouldn’t be much change in the viscosity of the system you talk about unless there is some water evaporation. See our post on salt curve analysis.

  33. sandeep

    Tetrasodium pyrophospate in what ph thick to liquied detergent.

    1. Perry Romanowski

      I don’t know. You have to test it in your specific formula.

      1. emmanuel

        Just one question on the salt curve determination 0 to 2% salt is refered to what?total weight of soap liquid or total weight of surfacant used?

        1. Perry Romanowski

          That’s the total weight of the entire batch, water, surfactant, salt and everything.

  34. Docblob

    Does it make a difference f I use sodium chloride or magnesium chloride as a thickener (in a SLES/LAO-System)?

    1. Perry Romanowski

      Sodium chloride would be better.

      1. nasrin

        why more electrolyte drops the viscosity drastically ?

        1. Perry Romanowski

          That’s just how nature works. If you put in too much electrolyte you reduce the ability of micelles to closely pack.

  35. ashish1234

    Hello to all,
    I have the following problem in shampoo!!
    I am making a shampoo formulation with following ingredients:

    1. Carbopol Aqua SF-1:6-7%
    2. SLES: 30% as supplied
    3. NaoH (for neutralization)
    4. CMEA:2%
    5. Cetyl alcohol:0.5%
    6. Laureth-4:0.5%
    7. Brij 35:2.5%
    8. CAPB:5%
    9.Amodimethicone:2%
    10. Sensomer: 0.1%
    11. Propylene glycol:3%
    12. Panthenol:0.6%
    13. Parfume:q.s
    14.Preservative:q.s
    15.Water: q.s

    The viscosity of the final formulation before addition of citric acid comes out to be 3000 cp at 5o/sec shear rate. The pH of the product is 7.5 before citric acid addition.The formulation is homogeneous without any air entrapment of foam. However when I add the citric (or even lactic acid) to the formulation to bring the pH down to 5-6, there occurs drastic change in viscosity and goes down to 800 cp. Moreover milk like curdling occurs during addition of citric acid and we don’t know how foaming occurs in the whole shampoo formulation even at low rpm’s. It is said that Carbopol Aqua SF-1 gives back acid thickening but in our case we are finding thinning of the system, sudden appearance of foam, milk like curdling and entrapment of air.!!

    Please suggest me what can i do to adjust pH in a way that original consistency and characteristic of shampoo are maintained and no air or foam entrapment occurs.What can be the possible reasons for this effect of pH on Carbopol Aqua Sf-1.!!

    Thanking you all and waiting for reply..!!

    1. nasrin

      whats brij and capb?

      1. Perry Romanowski

        These are types of surfactants

    2. sulastomo

      my suggestion there no effect of citric acid on carbopol aqua SF-1, it caused by Amodimethicone, because amodimethicone is very difficult to thicken. if you are still want using amodimethicone you should consider about pH, thickening agent (prefer polymer) if you are does not want using polymer you can emulsified amodimethicone with emulsifier and hydrotrop first then added into shampoo base.Process should be like this :
      1, 2, 3 soluble and melting at 70 oC
      1. SLES: 30% as supplied
      2. CMEA:2%
      3. Cetyl alcohol:0.5%
      4. Water

      added
      5. CAPB:5%
      6. Carbopol Aqua SF-1:6-7% + Water 5%
      7. Propylene glycol:0.5%

      Emulsifier
      8. Laureth-4:0.5%
      9. Brij 35:2.5%
      10.Amodimethicone:2%

      11. Sensomer: 0.1%
      12. Panthenol:0.6%
      13. Parfume:q.s
      14.Preservative:q.s

      15. NaOH (for neutralization) it’s better using Triethanol amine sensory feel better than NaOH.
      16.Water: q.s

      pH optimum at 4.5 – 6.5 for conditioner.

  36. Pingback:Dr Bronner Castile Dish Soap – with Salt (test #1) | Carol Drive

  37. Jerry

    Thanks for a very informative article.

    We are making an SLS and paraben free shampoo using a base (decyl glucoside, coco betaine). It is perfectly thick and works great EXCEPT when we add the fragrance it turns completely into water. Salt doesn’t seem to work. We’ve been using Xanthan Gum to thicken but in order to get a good viscosity we have to put in so much that the shampoo gets slimy.

    Any advice on thickening an SLS free shampoo like ours?

    (I’ve read that we can try and mix the fragrance with DPG (dipropylene glycol). Do you think this will help? Or is there something else we can do that may be easier/simpler? (I’ve even bought thickeners from various vendors to no avail).

    Thanks!

    1. Perry Romanowski

      You might try less fragrance or a different fragrance.

  38. Ghassan

    How do we raise the viscosity of shampoo during manufacturing?I have used the increase of salt and excessive amount of Coconut di ethanol It has got a temporary wife then disappear to become a new shampoo thin

    1. Perry Romanowski

      This really depends on what else is in your formula.

      1. Ghassan

        The combination shampoo normal adopted by simple they consist of: Lauryl sulfonic acid (solution 70%) + water + salt + dissolution within 24 h (with stirring violent) = output + Tri ethanol Amin + additions: glycerin + Conditioner + propylene glycol + materialportfolio + perfume + a few of methyl alcohol + iso propyl Merestat + silicon oil emulsion vitamin + Other Option depending on the nature of poetry.And finally the pH calibration.

    2. Ghassan

      Thank you
      But I have an additional question, please, can I replace the salt sodium chloride whith ammonium chloride salt in the same proportion?
      Can I use magnesium sulphate with Lauryl sulfonic acid to get the shampoo does not tear the eyes? And if so; does add salt (sodium or ammonium) or rest on it and realized viscosity too?
      Finally Can I use tylose the viscosity to raise? When can I hold added without that happening during the conglomerate added?
      Then what is the damage to the hair of this added?

  39. Frank

    Pls perry, i have made moisturizing body wash for more than 3 times now, but keep getting a thin result. This is my formula: water 72%, sles 15%, betaine 3%, HEC .5%, edta .2%, glycerine 2%, pearlizer 1%, sheabutter 2%, stearic acid 2%, castor oil 1%, citric acid, fo, preservative . But i find it hard thickening it. Pls how do i thicken. Or which thickener should i use?

    1. Perry

      You could increase the level of HEC (up to 1%) or reduce the amount of oil in the formula (less sheabutter, less castor oil). I would encourage you to do a knockout experiment to find out what is going on in your system.

  40. Pingback:Salt Curve Analysis – How to control cleansing cosmetics

  41. Jerome

    if you have a shampoo base that immediately looses viscosity upon adding salt or perfume, where do you go next?

    1. Perry

      That really depends on how much salt you’re talking about. There are two things you can do..

      1. Lower the amount of salt (or perfume) added
      2. Increase the level of surfactant & secondary surfactant

      It’s difficult to give exact answers to this question because it is very dependent on the type of surfactants used.

  42. Jerome

    Thanks for the Blog. Can you talk more about what you mean by the ratio of surfactants. Also, is it necessary to add something to stabilize the Micelles?

    1. Lourdes

      hi,
      i used excess amount of salt and it made my car shampoo thinner. to avoid loss in my production, how do i save this batch? i used sles, cdea as main ingredients. do i need to add some more sles or just water. pls help.

      1. Perry Romanowski

        See our article on saving batches. Basically, you make another batch with no salt and mix the two together in the proper ratio to get the thickness you want.

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