Shampooing should be as easy as wet, lather, rinse, repeat. But what nobody tells you is that shampoo goes on the scalp and conditioner goes on the lengths and ends.
The correct way to shampoo is to wash only the first 5 cm of the hair at the scalp where sebaceous oils, sweat and dirt gather. It really is not necessary to shampoo the lengths and ends of your hair as the shampoo that washes over the lengths and ends during rising should be sufficient to remove any dust, dirt and smog. As a matter of fact, washing your lengths and ends will only remove essential moisture and natural oils, leading to dried out ends.
Shampoo is formulated to open up the cuticles to ensure proper cleansing. Leaving those cuticles open will be disastrous as precious moisture and colour will seep from the hair. That is where conditioner comes in. Conditioner tightly closes the cuticle to prevent moisture loss, fight frizz and to help with detangling. When conditioning, you should use sufficient conditioner to cover the lengths and ends to ensure proper closure of the cuticle over the entire hair shaft.
That is also why it is important to ALWAYS use a conditioner after shampooing.
Also for this same reason, it is difficult to understand why people would want to use two-in-one shampoo’s and conditioners. Are you closing or opening the cuticle? Are you cleansing or moisturising? I am sure the hair shaft is just as confused as I am.
As a result, on long hair, you would be using more conditioner than shampoo and your conditioner would be depleted first. On short hair however, it would be a different story.