Hair and Scalp Care; Applied Sciences
Core concepts
Hair is composed of the cuticle, cortex, and medulla. The cuticle is the protective outer layer; the cortex contains pigment and gives strength and elasticity; the medulla is often absent in fine hair. The follicle is living tissue with a sebaceous gland and arrector pili muscle. Growth cycles are anagen, catagen, and telogen. Hair is mostly keratin and is not alive once formed. pH matters: skin and hair prefer mildly acidic products around pH 4.5 to 5.5; alkaline products open the cuticle. Porosity is the ability to absorb moisture; elasticity is stretch and return. Density is strands per square inch; texture is strand diameter.
Scalp and skin
Distinguish disorders such as dandruff and oiliness from diseases such as tinea, impetigo, and lice. Contagious or inflamed conditions are contraindications; refer to a physician. Do not diagnose. Analyze scalp and hair before every chemical service.
Traps
Medulla is not present in every hair. Dry hair is not necessarily damaged hair; high porosity absorbs and loses moisture quickly. Elasticity testing is not a diagnosis. Do not treat a scalp disease.
Worked example
A client’s hair feels rough and breaks when stretched. Wet a strand and stretch gently. If it snaps quickly, elasticity is low; avoid lightening and recommend conditioning. If it stretches and returns, proceed cautiously with a strand test.
Rule of thumb
When in doubt about a scalp condition, do not treat it; refer it.