Anatomy and Physiology of the Hair, Skin, and Scalp
Core concepts
Know the layers of the skin (epidermis, dermis, subcutaneous), the hair follicle, sebaceous glands, and arrector pili muscle. Understand the hair growth cycle (anagen, catagen, telogen) and that shedding is normal. Know the three hair types (lanugo, vellus, terminal) and the structure of the hair shaft (cuticle, cortex, medulla).
Traps to watch
Questions test that the follicle is the living part and the shaft is dead keratin. Do not confuse the growth phases: anagen is active growth, catagen is transition, telogen is resting/shedding. Know that sebaceous glands secrete sebum and are attached to follicles. The scalp has five layers (skin, connective tissue, aponeurosis, loose areolar, pericranium).
Worked rule of thumb
If a client reports sudden hair loss, it may be telogen effluvium (stress, illness, medication) and warrants referral-barbers do not diagnose.
Safety
Recognize signs of scalp disease (redness, scaling, lesions, pus) and refer rather than treat.