Structure of Hair
1. Cuticle Layer — Composed of keratinized scale-like cells arranged in the direction towards the hair tip. The cuticle layer of regular hair consists of 6-12 layers of overlapping scales (fine soft hair has 6-8 layers, coarse hard hair has 8-12 layers). This layer protects the hair from external damage, such as structural disruption. When the hair is wet, the cuticle scales swell and become more vulnerable to damage. (They open under alkaline high temperatures and close under acidic low temperatures.)
2. Cortex Layer — Made up of protein cells and pigment cells, it constitutes about 80% of the hair and is the main body of the hair strand. It contains the following bonds: salt bonds, sulfur bonds. Fibrous cortical cells are twisted like braids, providing elasticity, tension, and toughness. The natural color of hair (melanin) resides within the cortex layer, composed of two pigments: blue-black pigment and red-yellow pigment. The ratio and arrangement of these pigments determine the hair color.
3. Medulla Layer — Located at the innermost layer, surrounded by the cortex cells. It is formed by a sponge-like structure with vacuum cavities (determining the thickness or thinness of the hair). When the arrangement is tight, the hair is coarse and hard (some hairs may lack this layer).
Four Key Bonds of Hair:
1) Hydrogen Bond: Reorganizes under high temperature, breaks down when wet.
2) Salt Bond: Hair is healthiest when its pH level is between 4.5-5.5.
Hydrogen bond and salt bond break down when wet and can be recombined using hot air, lasting until the next rinse (affected by water and temperature, control these bonds during blow-drying).
3) Disulfide Bond: A strong bond that can break and reorganize (controlled during perming), determining whether the hair is curly or straight.
4) Amide Bond: Determines the shine and elasticity of the hair (only present in coarse and hard hair, not in fine soft hair).
Properties of Hair:
1 Physical: Elasticity, Tension, Stretchability
2 Chemical: Water Absorption, Drainage
PS: Healthy hair absorbs less water and drains well.
Damaged hair absorbs more water and drains poorly.
Hair Texture Analysis:
Healthy Hair: Untreated, tightly closed scales, good luster, easy to comb.
1. Oily Hair: Overactive sebum secretion.
2. Dry Hair: Lacks oil, dry without luster, hard to comb.
3. Normal Hair: Beautiful, shiny, resilient.
Damaged Hair:
1. Mild Damage: Color level 5-6, dry tips.
2. Severe Damage: Color level 8-10, loss of cuticle scales (high water absorption, if not blow-dried, the hair doesn't dry easily due to lost drainage ability.)
PS: Scales lift, fall off, no luster, no elasticity, tangles easily.
pH Value of Hair:
Hair pH value: 4.5-5.5
Shampoo: 6-6.5
Perm solution: 8-10
Conditioner: 2.8-3.5
Mask: 3.5-3.8
Straightening cream: 11-13
Hydrogen Peroxide: 3
Hair Dye: 9
PS: Alkaline opens the cuticle scales, acidic closes them.
Factors Causing Hair Damage in Daily Life:
1. Chemical damage (excessive perms and dyes)
2. Improper or inferior shampoo (incorrect washing method)
3. Sunlight ultraviolet radiation
4. Incorrect cutting and blow-drying
5. Sea water (alkaline)
6. Copper sulfate in tap water
Related Article: How to Understand the Key of Hair and Hair Care?