Science of Hair
Hair, nails and the epidermis are made of keratins. Keratins also heal wounds. Keratin is made up of dead keratinocytes from the hair bulb.
https://my.clevelandclinic.org/health/body/23204-keratin
The hair is made of 3 main parts: the cuticle, the cortex and the medulla.
Cuticle
The cuticle is the outer later of the hair strand. Its function is to protect the other layers. It’s made of 8-10 overlapping, translucent layers that should lay flat when healthy. It keeps the hair hydrated and flexible by minimising movement of moisture in the cortex. When the cortex is lifted, it makes hair more brittle and drier because moisture leaves the cortex. The cuticle is hydrophobic, meaning it won’t mix with water but will attach to other hydrophobic substances like oil.
The cuticle can become damaged by brushing and other commercial products that use chemicals such as dyes, especially products that use heat. Conditioner helps protect the cuticle by softening it, making it less brittle.
Cortex
The cortex makes up 75% of the hair strand’s weight. It’s made up of tightly packed keratin spindles held together by disulfide bonds, which are protein structures that keep hair in it’s natural shape, as well as making the hair stronger and more elastic.
The cortex is arranged from the smallest structure, the amino acids, up to the biggest structure, the cortex itself.
Melanin is stored in the cortex, which gives hair and skin its colour.
The cortex can be damaged by chemical products and heat products like straighteners, bleach and perming products that increase the porosity of the cortex meaning there’s more holes and cracks, as well as weakening and disorganising it.
Since the cortex is protected by the cuticle, damage to the cuticle can lead to the cortex being exposed, which can cause breakage, split ends, and make the colour dull and less glossy.
Medulla
The medulla is more commonly found in thicker, coarser hair. The medulla is mainly made up of fats and has lots of holes containing water, air and oils. Melanin can sometimes be found in the medulla of darker hair. Its main function isn’t known.
References:
https://www.hairknowhow.com/know-your-hair-structure
disulfide bonds: https://www.philipkingsley.co.uk/hair-guide/hair-science/the-biology-of-your-hair.html
Hair Texture
Hair texture or hair type refers to how thick the hair is. Each person’s hair type is unique but is usually put into 1 of 4 types. The type is then broken down into a, b, or c to refer to the hair’s porosity, curl pattern, length, density and width.
Type 1
Type 1 hair is straight hair. Straight hair has a round follicle because all the cells divide at an equal speed.
1a hair is completely straight and flat.
1b hair is straight but has a little bit of volume.
1c hair has a body wave and a few noticeable s-waves but not many.
Type 2
Type 2 hair is wavy hair.
Type 3
Type 4
https://www.medicinenet.com/what_are_the_four_types_of_hair/article.htm