Most conditioners fall into the category of surface acting conditioners. They are formulated to work on the outer layer or cuticle of the hair strand. Deep conditioners - the ones where you are instructed to keep on from 15 to 20 mins with a plastic cap and/or heat - contain ingredients that are humectants (moisture retainers).
Deep conditioners penetrate the inner core, the cortex, of your hair supplying moisture and protein. They also contain hydrating ingredients such as aloe, wheat germ and olive oil. These conditioners, are called pack conditioners, and are heavy and creamy in consistency.
Leave-in conditioners do not penetrate the hair strand, but are formulated to quickly coat the hair and protect it until the next washing. They are lightweight, and will contain lighter conditioning agents, which add little weight to the hair.
Each hair strand has three layers and the cuticle is the outer layer which protects them. The cuticle consists of scales that cover the hair strand.
Perfect new born cuticle
Everyday styling, combing/brushing, washing, and the strands simply rubbing against each other causes friction and raises the scales on the hair strand. Conditioners work by coating the hair strand, making the scales close against the strand smoother.
Cuticle with everyday wear and tear
When the scales on the hair strand become severely damaged via harsh chemicals, bleach, sun, etc. the hair strand is weakened, begins to break down and layer by layer the cuticle begins to disappear exposing the cortex layer which it once protected. Once the cortex is exposed, split ends appear and the hair eventually breaks.
Again, conditioning your hair is a way to keep the scales on the hair strand smooth and therefore protecting the cuticle. Also after conditioning, when the hair dries, it is coated with a thin film, and prevents static electricity from building up and 'frizzing' the hair.
Our hair carries negative electrical charges, ingredients in conditioners carry positive electrical charges. The negative charges attract to the positive charges, which cancel each other out and therefore reduces static electricity, again eliminating frizz.
The thin film left behind by ingredients found in conditioners like panthenol, amino acids and Vitamin B5 also help raised cuticle scales on each hair strand to lie flat, which enhances hair color creating luster and shine. Flat cuticles also make the hair strands smoother and detangling much easier.
Peace and Blessings...
*Pictures - P&G Beauty