Hair Care and Hairdressing: Cutting, Styling, Chemical Services, and Color
Structure and bonds
The hair has cuticle, cortex, and medulla; the cortex holds melanin and the side bonds. Disulfide bonds are the strongest and are broken by permanent wave solution and thio relaxers, then re-formed in the new shape. Hydrogen and salt bonds break with water and heat. The COHNS elements are carbon, oxygen, hydrogen, nitrogen, sulfur.
Cutting and styling
Know the difference between a stationary guide (builds weight) and a traveling guide (follows the previous section). Elevation and overdirection create length and volume; blunt lines build weight, while graduated and tapered cuts remove it. Razors and texturizing shears reduce bulk - avoid them near the scalp on fine or fragile hair.
Chemical services and color
Hair levels run 1 (black) to 10 (lightest blonde). Law of color: blue neutralizes orange, violet neutralizes yellow, green neutralizes red. Developer volumes and lift: 10 volume deposits, 20 volume lifts about one level, 30 volume about two, 40 volume about three to four - and 40 volume is never the choice for fragile or previously lightened hair. Thio relaxers must be neutralized (sodium bromate or hydrogen peroxide); hydroxide relaxers are not neutralized the same way - they are shampooed out, then acid-balanced and chelated. Always strand test; patch test aniline-derivative color 24–48 hours ahead.
Worked example
A natural level 5 client requests level 8. That is three levels of lift, so choose 30 to 40 volume with a strand test, and check porosity and prior color first. Common traps: believing 40 volume lifts more if left on longer (it only damages more), confusing hydrogen bonds with disulfide bonds, and skipping neutralizer on a thio service.