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Bar Soap Vs Liquid Soap and can I wash my hair with them?

June 1, 2009

This question came up at the Australian Science Festival and got me thinking.   Bar soap is one of the most efficient personal care products that you can buy. It is cheap to manufacture, it is easy to pack – in fact it required very little packaging, it is good at cutting through greases and a little goes a long way. Great for the green consumer!  However, while soap is a great staple of the environmentally conscious bathroom cabinet it can’t do everything and this is down to its chemistry.

Bar soap has been traditionally manufactured by taking a fat  (this is almost always vegetable derived these days) and reacting it with an alkali solution such as potassium hydroxide. This reaction is called saponification and results in the production of the soap plus glycerine and water.  Bar soaps made like this may have the produced glycerine scooped out before the bar is set or it may be left in to give some additional moisturising.

Soaps made like this are very cheap and effective and can be made at home with a bit of effort. However, this type of soap is not great for the hair as the bar will be very high in pH and the alkalinity will strip the oils from the hair leaving it dull. This type of soap will also react to with salts and oils in the hair to form a scum which is difficult to remove without copious rinsing. This may also leave the hair hard to manage and comb. The high pH and the rinsing issues may also irritate those people with sensitive scalps and that is why shampoo was developed, but more about that later!

The traditional bar soap can be made a little more nourishing by the addition of moisturising agents such as goats milk or other natural emollients.  While these may help to negate the drying effect on your scalp, your hair will still not glisten and shine as well as you may like.

Another way of making bar soap use synthetic detergents instead of using oils and saponifying them – The Dove bar would be one example. These have existed since the 1950’s and are formulated to be pH 4.5-5.5 to more closely match the skin. These bars contain surfactants that are great for the hair – one of the key ingredients of the original Dove bar – Sodium Cocoyl Isethionate has been found to help prevent dyed hair fading when used in place of SLES based shampoos.  These bars are harder to make at home due to their harder to find ingredients but would make a reasonable alternative to a liquid shampoo. The only down side is that syndet bars also contain emollients and moisturising ingredients which may again leave the hair shine free.  So, cleansing = YES, shine and good comb-ability = NO.

Liquid soaps can come in all shapes and sizes some of which are fine for hair while others are not. Liquid Castile soap is an old favorite in green circles. This is the name given to soap made by saponification of olive oil only the glycerine is left in. The Castile bit comes from the Spanish town where the practice originated.  This soap has very similar properties to the bar soaps made by the saponification process. It is very efficient at degreasing surfaces (hair and skin) and has a high pH so can leave the skin quite irritated. Also being a soap it will also be hard to rinse and can form complexes with dirt leaving your hair dull and hard to comb.  The one thing on liquid castile soaps side is the ability of the user to add some of their own bits to the mix. Because it is liquid you can add essential oils, some more nourishing bases oils or herbs as desired to create something special. Just keep in mind that the liquid soap does contain water so environmentally it will be less efficient to transport around than the bars.

Otherwise liquid soaps can be made from a wide range of other surfactants and end up resembling basic shampoos. These more mainstream liquid soaps can be made at home (with access to the right ingredients) and can work very well as basic shampoos as they foam, clean and rinse off easily.

So, can bar soap cover all of your personal care needs? Well, nearly but not quite.  I do know plenty of people who wash their hair with either traditional bar soaps or with Castile soap and have no problem.  Like with most things it is probably a case of try it, you might like it but I for one have not managed to find a bar shaped substitute for my favorite shampoo.  The hair is very different to the skin, it is dead once it comes out of the scalp so to keep it in tip top condition it needs some care.  The traditional soap bars may even damage the hair as they make it difficult to comb and leave it prone to tangling whereas shampoo’s are often developed to have some ‘wet combability’ benefit built in.  I would stick to a shampoo for the hair and soap for the rest of the body – horses for courses!


16 Comments leave one →
  1. livehappilyafter permalink
    September 1, 2009 5:05 am

    There is one and only soap to wash you hair with not just to clean but also as a therapy: 100% extra-virgin olive oil soap. It’s not the Castile soap you would find everywhere these days. You need to Google it and find soap-makers that specialize on making it. Greek and Turkish stores are a good place to look for these Old World treasures.

    • April 30, 2010 9:12 pm

      You should try LOLES olive oil soap for your hair. It is 100% Olive oil soap, no fragrance, no color and any artificial. Manufacturing of Loles olive oil soap takes 4 months.Their web adress is I am using this soap for a very log time, it helps to reduce hair loss. For daily use I am just washing my hair with it but if I need to make my hair done then I am using it with small amount of hair contioner.

  2. November 17, 2010 3:02 pm

    hair care should also be supplemented with oral vitamins and minerals, biotin helps a lot in making healthy hair ~”‘

  3. October 19, 2011 1:47 pm

    I wash my kids hair with handmade soap – their hair is shiny and scalp healthy. Recently my 12 year old went to Melbourne for a few days and used the motel ‘shampoo’. She came home scratching her head constantly and on closer inspection her whole head was flaking. After four days washing with goat milk soap and rinsing with apple cider vinegar she was back to normal – no itchies. We have the benefit of rainwater, and I understand that it works better with soap than highly mineralised water.

  4. diahha permalink
    November 4, 2011 8:38 am

    i use olive oil soap for washing my hair too. i follow with a diluted apple cider vinegar rinse and then rinse again. it works well on my hair. super shiny!

  5. July 2, 2012 12:14 am

    Glad to see you like soap made with 100% extra virgin olive oil. Our company makes bar and liquid soap using only one oil – certified organic extra virgin olive oil. We add organic essential oils for a subtle fragrance. Check out our website at

  6. July 17, 2012 8:23 am

    Forget about bar soap for washing hair: Bar soap is fine for washing the hands, face and body but hair needs a proper shampoo. Shampoos are specially designed for use on the hair and will not leave it dry and dull like soaps do. Soap leaves a residue behind and it’s high PH makes it unsuitable for use on the hair and scalp.

    • July 17, 2012 11:51 am

      Actually, John bar soap can be used as a “shampoo”. Read the label of commercially produced shampoo and you will be astounded at how much detergent is in it. Detergent strips the hair and scalp of natural oils, weakening the hair and drying the scalp. A high quality soap that is super fatted, natural and made with high quality ingredients will be a treat for your hair. Personally, I started using bar organic castile soap made with 100% olive oil about a year ago. My hairdresser noticed a significant difference in the strength and overall condition of my hair. It is shinier, my scalp doesn’t itch and has gotten thicker.
      If you don’t like using a bar, look for a similar composition in a liquid version of organic castile soap. The secret is to look for all natural ingredients, detergent free, and made primarily with olive oil. A nice combination would be one that also has oat, sesame, sweet almond and botanical essential oils. The soap will not lather like commercial shampoo because it is detergent free, but your hair will be cleaner and easier to manage.

      • RealizeBeautyEd permalink
        August 4, 2012 9:20 am

        The ‘secret’ is the pH. Soap (including castile) has a high pH usually and that is what is bad for the hair leaving it dull and brittle. An acidic or neutral pH is best and if you can achieve that with castile great but if not your hair won’t be lovely. Washing less is also a good way to go as the hair does clean its self to a large degree. Not using hairdryers and wearing a hat in the sun also help.

  7. Claire permalink
    October 4, 2012 2:52 am

    It is important to remember that not all soaps are made alike and there are literally thousand to choose from. I’ve used various types of bar soap as shampoo for years, and it can definitely be a suitable and even better alternative to the shampoos containing artificial degreasers normally found in stores.

    They key in my experience is don’t put anything on your hair that would make your skin dry and never use more than you need. It’s very easy to get too much lather with bar soap if you’re not familiar with washing your hair that way, and that can leave your hair too dry or too weighted down, depending on the soap. Always try any bar soap on your body first. I find that simple olive oil soaps (not liquid Castile soap, which will leave your hair dry and tangled if used in regular hard water) do the trick nicely.

    I’ve also found a few brands of glycerine based soaps which work reasonably well for hair when followed with a proper rinse. There are of course also specially made bar shampoos that contain lots of moisturizing oils, and you can find them at fairly reasonable prices at stores that carry ‘natural’ care items, or through small online based soap makers.

    Just shop around and do a little experimenting. People have been washing their hair for centuries with plain soaps before the SLS laden alternatives arrived on the scene, it just takes a little more work to figure out what works with your hair type.

  8. May 28, 2013 3:53 am

    I know this site offers quality depending posts and extra material, is there any other
    web page which offers these things in quality?

    • RealizeBeautyEd permalink
      May 28, 2013 9:19 am

      I am not sure what you mean.


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