Scientific Concepts: Anatomy, Physiology, and Chemistry
Core science you must be able to apply
Anatomy questions on this exam are rarely pure recall; they ask you to connect structure to treatment decisions. Know the layers of the skin-epidermis (stratum corneum, granulosum, spinosum, basale), dermis (papillary and reticular), and subcutaneous layer-and what each contains. The epidermis is avascular; the dermis carries blood vessels, nerves, collagen, and elastin. Keratinocytes produce keratin, melanocytes make melanin in the basal layer, Langerhans cells are immune sentinels, and Merkel cells relate to touch. Sebaceous glands are attached to hair follicles and are most active on the T-zone; eccrine glands produce sweat and are absent from the lips and nail plates. The acid mantle (roughly pH 4.5–5.5) protects against bacteria and water loss.
Chemistry: the pH scale is logarithmic, so each unit is a tenfold change. Surfactants have hydrophilic and lipophilic ends; emulsions mix oil and water; oxidation and reduction underlie many exfoliants and color products. Traps: “the dermis is avascular,” “sebaceous glands are all over the body,” and “pH 7 is acidic.” Rule of thumb: lower pH is more acidic and generally more exfoliating; higher pH is alkaline and can swell skin and hair. Worked example: a lotion at pH 3.5 is more acidic than the acid mantle and may sting, while a cleanser at pH 8 is alkaline and may disrupt the barrier.