Hair and Scalp Science: Practice Questions & Explanations

Hair growth begins in the hair follicle, specifically at the papilla — a small cone-shaped structure at the base of the follicle that contains the blood supply and nourishes the growing hair. The portion of hair below the skin is the root; the portion above the skin is the shaft. Damage to the papilla can affect or inhibit hair growth. Understanding the basic structures of the hair root (follicle, bulb, papilla) and the hair shaft is core hair science on the cosmetology exam.

The three main layers of the hair shaft are the cuticle (the tough, outermost protective layer of overlapping scales), the cortex (the middle layer that gives hair its strength, elasticity, and natural color through melanin), and the medulla (the innermost core, which may be absent in fine or very light hair). Most chemical services act on the cuticle and cortex. Knowing these three layers and their roles — especially that the cortex is where color and most chemical changes occur — is essential hair science.

The cortex is the middle layer of the hair shaft and contains the melanin (pigment) that gives hair its natural color, as well as providing most of the hair's strength and elasticity. Chemical services such as haircolor and perms work primarily within the cortex, which is why the cuticle must be opened to allow products to reach it. The cuticle is the protective outer layer, and the medulla is the innermost core. Understanding that natural color and chemical changes center on the cortex is frequently tested.

Pediculosis capitis is the technical term for an infestation of the scalp/hair with head lice. It is contagious and spreads through direct contact or shared items like combs, brushes, and hats. A cosmetologist who detects head lice should not perform the service and should refer the client appropriately, while ensuring tools and surfaces are properly cleaned and disinfected (or single-use items discarded). Recognizing common scalp conditions — and knowing which ones contraindicate service — is important hair-and-scalp science on the exam.

A cosmetologist should not perform a service when the client has an infectious, inflamed, or broken-skin condition of the scalp or skin — such as an active fungal infection (like ringworm), severe inflammation, open sores, or signs of infestation — because the service could spread infection or worsen the condition. In such cases, the client should be referred to a physician. Recognizing contraindications protects the client, the professional, and other clients. Distinguishing normal conditions from those that prohibit service is a key exam and safety skill.

Trichology is the technical term for the scientific study of hair and its diseases and care. (Dermatology is the study of skin, onychology is the study of nails, and histology is the study of tissues.) Cosmetologists apply trichology when analyzing a client's hair type, condition, and any scalp issues before a service. Knowing the correct '-ology' terms for hair, skin, and nails — trichology, dermatology, and onychology respectively — is commonly tested in the scientific-concepts section.

Before chemical services, cosmetologists perform preliminary tests to predict results and protect the client. A strand test applies the product to a small section of hair to see how it reacts (for example, how the hair takes color or responds to a perm/relaxer). For products that can cause allergic reactions, such as some haircolors, a patch (predisposition) test is done on the skin in advance to check for sensitivity. Recognizing the purpose of these preliminary tests is important hair-science and safety content.

Hair, the outermost layer of skin, and the nails are all composed largely of keratin, a tough, fibrous, insoluble protein. Keratin gives these structures their strength and protective qualities. This shared composition is why hair and nails are both classified as keratinized structures. (Collagen is a structural protein of the dermis; hemoglobin and insulin are unrelated body proteins.) Recognizing keratin as the common protein of hair, nails, and the skin's surface links several scientific-concepts topics tested on the exam.

Alopecia is the technical term for abnormal hair loss, which can have many causes. (Trichology is the study of hair, pediculosis is a lice infestation, and canities is the technical term for gray hair.) Cosmetologists may notice signs of hair thinning or loss during services; while they can recommend gentle care and suitable styles, diagnosing the cause of significant or unusual hair loss is outside their scope and may warrant referral to a physician. Knowing the term alopecia and related hair conditions is tested hair science.