Our hair is composed of a cortex - the internal bit that gives strength to the hair fibre - and the cuticle - the chemically resistant outer layer. The cuticle is 6 to 10 layers thick, and its job is to protect the cortex from damage. It resists chemical damage by UV radiation and the environment, and resists physical damage by pulling, friction, and bending.
If you look at the picture, you'll notice that the cuticle is made up of overlapping scales. In an ideal world, these scales lie flat, reflecting light and giving us that wonderful shine we all want on our hair. The flat scales allow the hair to slide against other strands smoothly.
But the cuticle can resist damage for only so long! We treat it so roughly - heating, drying, dying, perming, and so on, and it responds by not laying flat, which leads to dull looking hair and damage to the hair strand. Scales from the cuticle can be removed, exposing the cortex, which can lead to serious internal damage.
A lot of the damage done to hair is about friction and abrasion. The damage that comes from dying your hair is both chemical and mechanical in nature. When you dye your hair, you are depositing colour, colour that can cause more frictional forces in your hair, which will increase the force required to comb your hair. This leads to cuticle damage. When you perm, your natural disulphide bonds are broken then re-formed in a nice curl (as a note, this is true of straightening your hair chemically as well). This leads to swelling, reduced cortical strength, and increase in friction. Heating our hair is damaging as well - excessive temperatures from curling or straightening irons can lead to a reduction in tensile strength, which weakens your hair.
Chlorine from pools is extremely damaging to hair. It can create bubbles of dissolved protein in the cortex, which burst through the cuticle and crack it. Salt water isn't as bad - it doesn't change the chemistry of your hair, but leaving the salt on the strands can lead to abrasion of the cuticle. (Which makes you wonder about those conditioners or treatments advertising certain types of salt inside!)
If hair is damaged by friction and abrasion, doesn't this mean that even brushing your hair can lead to damage? Yes. Remember when we were told to brush our hair 100 times to increase shine - yeah, the opposite effect is what you can get if you have too much friction!
When formulating a conditioner, you'll notice a lot of the ingredients talk about reducing wet combing forces. Wet hair has far less resistance to combing forces and friction than dry hair. One study estimated that wet combing unconditioned hair twice a week would result in serious cuticle damage in 14 to 60 months. (Yeah, it's not that accurate and there weren't a lot of definitions, but I do think it has a point - wet combing is not a good idea). And ingredients that reduce the forces for combing wet hair reduce the forces for combing dry hair - which is a very good thing - so we want to include lots of those in any conditioner or leave in conditioner!
Again, the key to formulating a good conditioner is to remove the static electricity, increase lubricity, and reduce the combing forces and friction. We do this by choosing a good cationic quaternary compound as our starting point, then add the ingredients that will help keep our hair healthy, repair damage, and help with other concerns we have, like frizzing or curling the wrong way or not laying flat.
Join me on Monday for a look at Incroquat BTMS.