The cuticle is the outer layer of your hair. If you look at healthy hair under a microscope it looks like shingles on a house - flat and tight. To the naked eye the tightly closed cuticle gives hair it’s shine. On unhealthy hair the cuticle is open and appears dull, lifeless, and stiff.
The cuticle is composed of a transparent, scale-like single layer of overlapping cells. The function of these overlapping, shingle-like scales is to protect the cortex which is immediately below the cuticle. The cortex is where your hair color resides. To color your hair the cuticle must be penetrated whether you are lifting or depositing color.
Opening the cuticle as little and as gently as possible is very important. If too strong a formulation is used the cuticle cannot ever close again and the color will leach out. This is why your box color which is formulated far more strongly than anything I would ever use in the salon, fades so very much. Box color assumes hard to cover gray and is formulated with a worst case scenario in mind. Using Steam to gently open the cuticle and a mild color formulation; the cuticle can close and thereby retain the color.
This is why I always rinse using cold water. Heat opens the cuticle - cold closes. The same rule applies to the blow dry.
Products with a high pH cause the cuticle layer to swell and allow liquids to penetrate into the cortex fading your color. Products with a low pH will cause the cuticle to shrink and harden. Make sure you always use a shampoo for color treated hair that has a low or balanced PH.
Conditioners temporarily give the illusion of heathy hair by filling in the open spaces but make the hair too heavy and soft. They do not bond to the hair. Some people mistakenly believe that conditioners are like vitamins for you hair. They are not. They all shampoo out. Furthermore, rinse out condoners soak the roots, as well as the shaft, making them too soft defeating natural body and lift. The roots are the healthiest part of your hair and they are what give your hair body and lift. Rinse out condoners tend soak the entire head and make the roots too soft, defeating body and lift. Many of my clients with fine limp hair already know this and do not use a rinse out conditioner but still need something to improve the appearance of the hair shaft. While there are many leave-in conditioners on the market, my Weightless Wonder (trademarked and copyright 1997 ian north) is better than any other. And it’s free to my clients.
Rarely, some women with exceptionally thick hair may wish to use a rinse out conditioner so that their hair is diminished in appearance. Or if the hair is too stiff they might use it make it more manageable.