Why conditioner or oil on length before washing?

[DarleneH]

I've seen people mention putting oil or conditioner on the length part of them hair before washing. What does that do? Because it seems to defeat the goal for moisturized hair, which you'd think is get water on it and then seal the water to the hair strands with the oil or conditioner afterward. I get the concept of using light conditioners on dry scalp for a conditioner only wash, but I don't understand what conditioner on dry length does?

[panffle]

Helps protect the hair from shampoo. You condition the length, shampoo, then condition again. Or oil, if you prefer that.

[DarleneH]

So if you're a COer and not a shampooer, it really doesn't do anything?

[spidermom]

Essential fatty acids are part of the chain of molecules that make up hair. EFAs erode away over time and oiling (oils that penetrate) replaces them. For shiny flexible hair, EFAs are essential.

[czech it out]

When I oil my hair before washing it, the parts that have been bleach damaged in the past come out silkier and don't feel as frizzy/dry. I think the oil also has a moisturizing effect on my undamaged hair, but it's definitely more obvious for me on the bleach damaged parts. Not sure why it works (like you said, it's a bit counter-intuitive), but it definitely does for me.

[torrilin]

For starters, it isn't necessarily going on dry hair. Depending on the product and your hair type, it may be better to apply product to dry hair or wet hair. In my case, either can work, and which I choose depends on convenience. For other posters, one or the other might be clearly better.

All the other reasons given upthread can apply too. Keep in mind that someone doing conditioner only washes is still washing with surfactants, just like someone who shampoos. They're considered milder surfactants, but using a second product as a surfactant buffer is still going to work.

Also, sometimes surfactants work to improve product absorption rates. Sounds weird I know, but it happens with a lot of different things. This is why a lot of box hair dyes will foam when you apply color. That foaming is due to a surfactant, and that helps the dye absorb. You can use the same principle with conditioning ingredients. Generally the surfactant is working to improve absorption rates by raising the outer keratin scales on the hair's surface. Water can cause the hair shaft to swell, and that will raise the outer keratin scales too.

Curly hair tends to be fairly porous, and it tends to absorb products better. The curlier the hair, the less smooth the outer layer of keratin scales are. Straight hair tends to have a smooth, tight layer of keratin scales so it's less porous. Chemical damage on any hair type will tend to damage the keratin scales and increase the porosity. Obviously, not all straight hair will have the same porosity, and some curly hair will be less porous than the most porous straight hair. Nothing natural is totally uniform , and there will always be variation.

So a curly person who has fairly porous hair naturally may choose to apply products to dry hair to minimize damage to the outer keratin layer from water and surfactants. Someone like me with straight and pretty non-porous hair that's also very dry may worry much less about preventing damage in that way, and a lot more about opening the keratin scales enough for products to work. Most of us are going to be more in the middle, so a wide variety of methods will work.

[sakuraemily]

torrilin and spidermom have given good answers.
Oil prevents shampoo from drying out hair too much