In my search for an answer I came across a post on thebeautybrains.com which contained a letter from a trichologist Barry J Stevens who described deep conditioning as 'wishful thinking' . I don't really know the authenticity of this letter but it made me even more interested to find out the fact from fiction.
First step, what really happens when you condition your hair? If you use shampoo, then what you first do is remove excess oils and grease from your hair leaving you with a clean shaft. What DOES NOT happen is 'opening of the cuticle'. I thought I should draw some of this out, just incase people's eyes start glazing over.
What can open up the cuticle? Commonly, chemical processing of hair such as relaxing or colour rely on alkaline products and these CAN open up the cuticle. Your average shampoo does not have the ability to do this. They are mostly mildly acidic to neutral (around pH 6-7 though 8 is considered ok) because cosmetic scientists need to consider that the shampoo can end up in your eyes, face and mouth, so it is safer to be close to neutral. See this site for some pH ranges of shampoo. Lisa Akbari also advertises a shampoo at pH 5. The pH of hair and skin is a range between 4.5 to 5.5.
Therefore, if your hair is natural, you most likely have a closed cuticle as has been seen scientifically (Khumalo et al, Journal of the American Academy of Dermatology, 2000, pp 814-820).
This leads to the question, if the cuticle is closed then what can really get in? Well two things can, water and some oils. What kind of oil can get into the hair cortex? The complex answer is many different oils to varying degrees. The simple answer is coconut oil and olive oil have been shown to penetrate hair quite well (Hornby et al, Int Journal of cosmetic science 2005 pg299-300).This now leaves the question, what exactly is the purpose of conditioner? Well most conditioners do just work on the outside. They soften the hair, help smooth the cuticle, minimize static, sometimes help the water stay in the cortex. When rinsed off they do leave some conditioning agents behind which keep the hair feeling soft. So why do so many people say that deep conditioning is good? Well maybe they just have a better procedure and can get more out of it.
1. Make sure you have sufficient water, make sure you wet your hair properly and make sure your chosen conditioner has coconut oil or olive oil. If it doesn't, consider adding a teaspoon or so to it (portion out the part you are going to use and add the oil to that, do not put it into the main container).
2. Concentrate on applying the conditioner very well so as to cover your all your hair. Don't plop the conditioner onto the middle of your head, back and sides. Take your time, part the hair and apply to small sections.
3. Do you need heat? It takes 15 min for hair to get saturated in pure water while steam takes 18 hours or more (Robbins, Chemical and Physical Behaviour of Human Hair, Springer). Water directly on your hair through wetting is probably more useful than steam or vapour.
4. Should you leave it on for longer? Well you can do so if you want to, but if you leave it just for the stipulated time, then you don't need to worry too much.
So is deep conditioning a myth, what do you think?