The Drawbacks of Shampoo Bars

When used in soft water, soap can generate a nice lather and leave hair feeling very soft and clean. In fact, in really soft water and after using an extremely moisturizing soap, the soft and slippery texture of our skin and hair can feel so foreign to us that we may continue rinsing repeatedly in an attempt to remove the perceived residue.

Unfortunately, soap’s effectiveness is significantly reduced when used in hard or acidic water. The reason for this is that the carboxylate group on the soap molecule interacts preferentially with the metallic ions that are so prevalent in hard water (usually calcium, iron, and/or magnesium). The result is the formation of a precipitate, which leaves an insoluble film on whatever surface comes into contact with it, including the hair. This film can be very difficult to remove and leaves the hair dull, lifeless, tangled, and dry. The soap lathers less and cleanses less effectively for the same reason: two soap molecules are removed from action by each magnesium or calcium ion when the complex is precipitated from the solution, so there is less soap available for cleansing. That squeaky clean feeling you may get after using a bar soap is actually the feel of organic/mineral deposits on your hair shaft. This deposit left on the hair can also attract dirt, making hair greasy and dirty. This problem was one of several driving forces for the development of synthetic surfactants such as sodium laurel sulfate.

Another potential hazard of the shampoo bars and soaps is that they typically have a pH in the 8 to 9 range, which is substantially more basic than the natural level for hair. This can result in a temporary breakage of disulfide bonds in the keratin protein of the hair, which can disrupt curl formation and cuticle structure. The basic environment softens the hair, swells it, and leaves it with a ruffled cuticle. This rough surface is not only a source of potentially damaging entanglements and breakage, but also is unattractive because it reduces the shine and gloss of hair tremendously. Swelling of the hair also enables larger colorant molecules to escape, which can shorten the lifetime of a coloring application.

Fortunately, there are a few things you can do to counteract these two effects. Some soap makers put various additives in their soaps that help to keep the soap molecules from binding with hard water metals (sodium silicate, sodium carbonate, borax). However, in the “all-natural” products this is not likely, so it is important to take some steps after shampooing. Rinsing with a mildly acidic solution will help dissolve the soap scum deposit from your hair, shrink the hair shaft diameter, flatten the cuticle and increase the shine and smoothness of your hair. White vinegar, apple cider vinegar, or dissolved citric acid or vitamin C (ascorbic acid) all have sufficiently low pH to help return hair to its preferred pH pf approximately 4-5. Using a clarifying shampoo with EDTA in it can also help remove build up, but would also involve use of a more harsh surfactant, so might be best done only occasionally.

You can also try washing your hair in bottled, purified water when you use your soap, which would make this step necessary less often. Another option is getting a showerhead filter, which is generally less expensive than a whole-house water softener. Even if you take these steps, it is wise to do a mild acidic rinse, due to the basic properties of the soap. Also, dirt on your hair can have minerals in it, which can then create soap scum, so you can’t avoid the need for the low pH rinse entirely.

Depending upon the composition of the soap you are using, the condition of your hair, and the type of water you have, you may find you need to use less conditioner than when you use other cleansers. Experimentation will help you figure out what helps your hair look and feel its best.


How can I incorporate shampoo bars into my hair care routine?

  • Look for one with the plant-derived oils which you prefer, or buy a few bars and try different recipes.
  • Lather the bar in your hand, not on your head. Your hair is as fragile as a cashmere sweater, and needs very careful handling at all times.
  • Use soft water to wash your hair with soap bars whenever possible.
  • Follow up with a mildly acidic rinse to restore the natural pH of your hair and to impart that shiny, glossy surface we all desire.
  • Use detangler or conditioner to your own personal tastes. In other words, if you still feel you need it, go ahead! I personally wouldn’t skip that step unless my hair looked weighed down or limp.
  • Give it a few tries. I have read that it can take some time for your scalp and hair to adjust, just as it often does when you go to a low shampoo or shampoo free routine.
  • Report your results to us!

I plan to head to my local health food store soon for some shampoo bars, or maybe don my chemist gear and make some myself!

Additional reading about pH and hair is available here.

Email your questions to Tonya.

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Has this been edited, or the old article removed? I thought that the Curl Chemist said she did NOT recommend using these bars. If she has changed her opinion, I might be willing to try them.
What defines "soap"? This is not clear to me. Thanks.
I've read this before but just realized the whole "Protein" issue with the bars and the need to "clarify" also with more than just ACV TY!
Awesome info !! It is great to have an easy to understand article that answers so many questions that have been posted on the boards. Thank you very much!!
Wonderfully informative article. It explains why my hair doesn't seem to like the bars: hard water, color-treated (it faded).... I wonder if it's possible to add some vinegar to the water with which I rinse the soap out. ???
Wow - amazingly informative - technical yet thoroughly palatible to us non-pros. Well done! Thanks.
Thanks so much for answering my questions and more! I feel much more confident trying out some shampoo bars now that I know what they're actually doing to my hair. I found it especially helpful that you gave some suggestions on how to start using them, just what I needed! Thanks again!