Comprehensive Notes on Hair Science for Cosmetologists

Definition of Porous Hair: Refers to hair that allows water to enter and then come back out. This characteristic is important for hairstylists to understand.
Porous Hair Type: Natural hair is identified as being porous. Knowing this allows for clear communication among hairstylists about specific hair types.

Consultations: The most important part of any hair service. Consultations are crucial for understanding client needs and managing expectations.
Key Consultation Questions: Hairstylists should ask specific questions tailored to the client to gather necessary information.
Patch Testing: Particularly important for new color clients. A patch test ensures the client is not allergic to the product, preventing adverse reactions.

Etymology: The term "trichology" comes from the Greek word "trichos" meaning hair, and "ology" meaning the study of.
Integumentary System: Hair, skin, nails, and glands are all integral components of the integumentary system.

Client Concerns: Clients frequently express concerns about hair thinning or feeling like they have less hair.
Understanding Hair Cycles: It is essential for hairstylists to understand the natural cycles of hair growth and shedding. This knowledge allows them to reassure clients that normal hair fall is not indicative of balding.
Educational Role: Hairstylists can reinforce to clients that their hair is likely not falling out abnormally, but rather going through its natural cycle.

Hair Follicle: This is the entire area from which the hair grows.
Arrector Pili Muscle: This muscle is responsible for causing hair to stand on end (e.g., goosebumps).
Sebaceous Gland: Each hair follicle has its own sebaceous gland, which produces oil (sebum) to lubricate the hair and scalp.

Three Main Parts: The hair shaft consists of three primary layers:
- Cuticle: The outermost layer of the hair. It resembles fish scales or shingles on a roof, with layers lying on top of each other.
  - Function: The cuticle is what makes hair look shiny and feel smooth.
  - Stylist Importance: Maintaining the integrity of the cuticle layer is crucial for healthy-looking hair. Damaged cuticles lead to dull, rough hair.
- Cortex: The middle layer, located inside the cuticle.
  - Function: This layer contains all the pigment of the hair (melanin). It is also where all chemical reactions occur during services.
  - Stylist Importance: When coloring, chemically straightening, or chemically curling hair, the chemical processes primarily happen within the cortex.
  - Melanin: Specific pigments within the cortex that give hair its color. Different types of melanin will be discussed in more detail later.
- Medulla: The innermost layer, located inside the cortex.
  - Stylist Importance: The medulla generally does not hold significant importance for hairstylists in their daily work. Not all hair types or individuals have a medulla.

Acronym: The chemical composition of hair can be remembered using the acronym "COHNS."
Primary Component: Hair is approximately $90\%$ protein.
Elemental Composition and Percentages:
- Carbon ( $\text{C}$ ): $51\%-54\%$
- Oxygen ( $\text{O}$ ): $21\%-24\%$
- Hydrogen ( $\text{H}$ ): $6\%-8\%$
- Nitrogen ( $\text{N}$ ): $15\%-17\%$
- Sulfur ( $\text{S}$ ): $3\%-6\%$
Importance: These elements and their percentages are critical information and will be included on the test.

Nutrient Prioritization: The body prioritizes essential functions. It first ensures that muscles, organs, and other vital systems receive necessary nutrients.
Leftover Nutrients: Only any leftover nutrients are then directed to the hair. This illustrates why hair health can often reflect overall body health or nutrient deficiencies.

Test Format: Most tests will consist of multiple-choice, true/false, and matching questions.
Written Responses: Some questions will require written responses, but extensive essay-style answers will be avoided, especially in earlier semesters.
Assignments: In the third semester, students will be required to submit larger assignments.