Deep conditioning: Curl definition and Damage?

A specific comment on the original deep conditioning post says that deep conditioning produces excellent curl definition. The panel were presented with  one theory on why this happens ( BBA,pp 210-216,1999). This study suggested keratin changes structure when exposed to water for long. For example a study on nails (same keratin type as hair) showed that protein (keratin) coiled very differently after 15 minutes (saturation point of water). This coiling change led to softening and weakness in the keratin.  The panel were asked

1. Do you think that curl definition associated with deep conditioning could be linked to temporary changes in keratin
2. Do you think it is beneficial or do you think there should be a time limit on water exposure?

Jc: Yes it may increase definition but this could be damaging
Nails and hair have same type of keratin, therefore I think that this link is valid (meaning water changes the keratin pattern). I do not think it is right to avoid water but I do think some regimes can be quite extreme for example leaving the conditioner on overnight. I think repeating this regularly could lead to softer but weaker hair. Weak hair breaks.

Ktani: Hair recovers well from water 
"The bonds that link up the polypeptide chains of the hair are hydrogen, salt and disulfide bonds. Hydrogen bonds account for one-third of the hair's strength. The hydrogen bond is a weak physical side bond that is easily broken by water or heat. Hydrogen bonds can be reformed by drying or cooling the hair." Hair recovers from water very well without damage. Source:

Monique: Curl definition is not just about product
I was going to quote a similar fact that Ktani stated regarding hydrogen bonds in hair. They can be temporarily broken by water (hence the various styles we achieve from braiding/twisting while wet), they reform when the hair is dry. However, I believe that these hydrogen bonds are broken when some type of physical change is placed on the hair - typically via styling. I don't agree that DC will yield excellent curl definition by sole application of the product. I do believe that DC can smooth the hair cuticle - this smoothing naturally causes curl definition for some. In the case of some conditioners, more time yields more penetration or deposition onto the hair follicle. I do think there is a point at which using extended time periods to DC your hair is excessive.

Noire: Yes hydrogen bonds in hair can be broken by water 
I would agree with the responses, especially that hydrogen bonds can be broken by water. It is known that hydrogen bonds make up the amorphous matrix of hair and nails, the above is a valid point. Ref: H.P. Baden et al (1973)

Laquita: Conditioner does have a role in curl definition  
I also think this point is valid and depending on one's hair type conditioner alone does define curls. I pretty much get the same curl definition with water as I do with conditioner, but with conditioner the definition stays longer and curls/waves are elongated, and with water once my hair starts to dry the definition goes away as my hair shrinks. I think using conditioner to define curls can be beneficial for those whose goal is to do so, but I think there should be a time limit and/or care should be taken as to the amount of conditioner used. I believe the conditoner should be diluted with at least 80% water if it's going to be left on the hair for extended amounts of time or used as a styling agent.


  1. Then what do you think about the conditioner only method that is so popular on ytube, hair forums and hair bloggers.
    The styling method involves leaving undiluted silicone based conditioner in hair for a week at a time. Terri, who is the owner of the site and has even written a book about the method, has grown her hair to tailbone length using it and believes it works to protect and strengthen the hair rather than weakening it.

  2. @Ktani
    1) how about hydral fatique
    2)Can we have a more precise source than this :

    @ JC

    I'm not one to know if a scientific source is really scientific or not, can you let us know if the sources are peer review or credible for this post and the previous ones ? Thanks

  3. Dea- I do not think that Terri's method of using hair conditioner is the same as deep conditioning. The conditioner is expected to dry on the hair and is therefore used as a styling product. I am speaking in reference to people who will actually apply the conditioner and keep it moist by wrapping a plastic cap and sleeping in it overnight then wash it later the next day.

    Also just because Terri has long hair does not mean that others using the method will equally gain long hair. I keep emphasizing that everyone has to find a method that works for their hair. For some Terri's method will be great for others it won't.

    I personally would discourage overnight deep conditioning but I am certain some people will feel that they have had succes with it. So remember the purpose of the site is to encourage you as an individual to make your own decisions, not to promote one form of hair care.

    Kadiane - Ktani did provide a full reference but I chose to highlight the texascollaborative site. You can simply search for hair and hydrogen and you will get to the result page. I think texascollaborative is a good basic site and is fairly informative as a general source.

    My personal preference as I have previously written is for peer reviewed journals. I do however think that sites like the loreal hair science site and texascollaborative site are informative.

  4. When I immerse my nails in water for a prolonged period I have also noted the softening effect that this can have on the nails. However I have found upon drying, my nails feel like they have returned to their former strength -- i.e. the softening/weakening effect is only temporary as you stated. I have done this repeatedly and do not believe that I suffer from weak nails.

    So why is it that you would apply the same theory to hair with the exception that when it comes to hair the weakening effect would be permanent? And does softer hair really mean weaker hair?
    Here is another link of a natural wih beautiful healthy long hair who says she deep conditions overnight regularly. I think her name is Chima if the fotki link does not work.

    Anyway keep up the good work with this blog even though I may not understand this theory you give useful information, clarify myths and produce an environment conducive to learning and healthy debate.

  5. Anon - Please note, I am NOT saying the damage to the nail is temporary, I am saying it is permanent. The issue of permanent damage to the keratin arises when nails are exposed to water for long periods and frequently.

    This is not the temporary softening cycle that you are talking about. The permanent damage arises from repeating that softening cycle and also from prolonged water exposure.

    As per my answer to Dea, I think you should develop your own hair care method because your hair is individual.


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