Hair, skin and pH
A hair strand has three layers: the cuticle (clear, overlapping scales on the outside), the cortex (keratin fibres and melanin, which give strength and colour) and the medulla (soft core, sometimes missing in fine hair). Skin has a thin protective layer called the acid mantle.
What pH means
pH tells how acidic or alkaline something is, from 0 to 14. 7 is neutral. Below 7 is acidic; above 7 is alkaline. Each step is ten times stronger than the next.
- Hair and skin: about pH 4.5–5.5 (slightly acidic).
- Conditioner, acid rinse: pH 3.5–5 (closes the cuticle, adds shine).
- Most shampoos: pH 5–7.
- Permanent colour, perm lotion, relaxer: pH 9–14 (swell the hair and open the cuticle).
After an alkaline service, use an acidic (pH-balancing) product to close the cuticle again. Too much alkaline treatment leaves hair dry, frizzy and weak.
Chemicals, allergies and safety
Some ingredients can cause allergic reactions (redness, itching, swelling) or irritation:
- PPD (para-phenylenediamine) and PTD in permanent hair dyes, and in some dark 'black henna'.
- Ammonia and hydrogen peroxide in colour and bleach.
- Thioglycolates in perms and some hair removal creams.
- Fragrance, preservatives (like parabens or formaldehyde releasers), nickel in tools, latex in gloves, and acrylates in nail products.
Safe practice
Do a patch test (skin allergy test) 48 hours before every colour service. Read safety data sheets and labels, wear gloves, keep the room ventilated, store chemicals closed and labelled, never mix products that the maker says not to mix, and disinfect tools between clients.
Tools, products and services
Tools: combs and brushes, scissors and thinning shears, clippers, blow-dryer, flat iron and curling tongs, rollers, sectioning clips, colour bowls and brushes, nail files, make-up brushes and sponges.
Services: shampoo and conditioning, scalp treatment, cutting, blow-drying, setting, braiding and up-styles, colour and highlights, perms and relaxing, facials, manicures and pedicures, and make-up.
Hair and scalp analysis
Before any service, check: texture (fine, medium, coarse), density (how many hairs), porosity (how fast it soaks up water), elasticity (how far a wet hair stretches and returns), growth patterns (cowlicks), and scalp condition (dandruff, dryness, cuts, lice). If you see an infection or open sores, do not perform the service and suggest a doctor.
Design, colour theory, trends and make-up
Elements of design: form (overall shape), space, line (straight or curved), texture and colour. Principles: balance (even or uneven), proportion, rhythm, emphasis (a focal point) and harmony.
Colour theory
Primary colours: red, yellow, blue. Secondary: orange, green, violet. On the colour wheel, opposite colours neutralise each other: violet toner cancels yellow, blue cancels orange (brassiness), green cancels red. Hair colour has a level (1 = black to 10 = lightest blonde) and a tone (warm or cool).
Face shape and purpose
Choose shapes that balance the face: add height for a round face, add width for a long face. Match the look to the purpose: everyday, bridal, stage, photo or cultural styles such as braids, buns or headwraps, and respect the client's traditions.
Make-up
Prepare the skin, match foundation to skin undertone, use light to bring features forward and shade to push them back, and keep day make-up softer than evening or stage make-up.
Clients, records and business
Professional behaviour: be on time, clean and polite, listen first, keep client information private, and work as a team.
The consultation form
It records contact details, allergies and medical notes, hair and scalp analysis, the look the client wants, products and timings used, and the patch-test result. It protects the client (safety), the stylist (proof of what was agreed) and helps repeat the result next time. Build a client profile from it.
Maths and reading at work
Read instructions and labels carefully. Mix colour by ratio: a 1:2 mix of colour to developer with 40 mL colour needs 80 mL developer. Time processing with a timer. Work out prices, discounts and tax.
Advertising and display
Use social media posts, before-and-after photos (with permission), loyalty cards and clean, well-lit window or shelf displays grouped by colour or use. Keep up with new products and tools through trade shows and training.
Try it: test pH at home
With an adult, dip pH paper (or red-cabbage water) into shampoo, conditioner, lemon water and soap solution. Note the colour and pH. Which would close the cuticle? Which would open it? Check your answers on the pH slider in the last 3D step.
Key formulas and definitions
- pH < 7 acidic · pH 7 neutral · pH > 7 alkaline
- Hair and skin ≈ pH 4.5–5.5
- Alkaline (pH 9+) opens the cuticle; acidic closes it
- Opposite colours neutralise: violet↔yellow, blue↔orange, green↔red
- Mix ratio: developer = colour × ratio (1:2 → 40 mL colour + 80 mL developer)
- Patch test: 48 hours before every colour service
Worked examples
1. A client's blonde hair looks too yellow. Which toner should you use and why?
Violet. Violet is opposite yellow on the colour wheel, so it neutralises the yellow tone and gives a cooler blonde.
2. A colour needs a 1:1.5 mix. You use 60 mL of colour. How much developer?
Developer = 60 × 1.5 = 90 mL. Total mix = 150 mL.
3. A client had colour last year with no problem. Do you still need a patch test?
Yes. Allergies can develop at any time, even after many safe uses. Do a patch test 48 hours before every colour service and write the result on the card.
Common mistakes
- Skipping the patch test because the client 'never reacted before'.
- Leaving hair at a high pH after colour without an acidic conditioner, so the cuticle stays open and hair turns dry.
- Choosing a toner from the same side of the colour wheel instead of the opposite colour.
- Not filling in the consultation form, so there is no record of allergies or products used.