Scientific Concepts: Anatomy, Physiology, Chemistry, and Infection Control
Anatomy and physiology
Know the layers of the skin (epidermis, dermis, subcutaneous) and what lives in each: the dermis holds blood vessels, nerves, sweat glands, and sebaceous glands, which is why a service that reaches the dermis can break the skin barrier. For hair, be able to trace the follicle: bulb, papilla (blood and nerve supply), sebaceous gland, arrector pili muscle, and the three growth phases (anagen, catagen, telogen). For the head and face, expect questions on skull bones (frontal, parietal, temporal, occipital, zygomatic, maxilla, mandible) and the two key nerves: the fifth cranial (trigeminal), which supplies sensation, and the seventh (facial), which supplies the muscles of expression.
Chemistry
pH drives most chemical services. Below 7 is acidic, 7 is neutral, above 7 is alkaline; skin and hair sit around 4.5-5.5. Alkaline products swell the cuticle and soften hair; acidic products contract and harden it. Know the side bonds - disulfide bonds are broken by perms and relaxers and rebuilt by the neutralizer; hydrogen bonds are broken by water and re-form on drying; salt bonds are broken by pH change.
Infection control
Separate cleaning (soap and water, removes debris), disinfection (EPA-registered hospital disinfectant, kills most pathogens on nonporous surfaces), and sterilization (destroys all microbial life, including spores). Know pathogen groups: bacteria (cocci, bacilli, spirilla), viruses, fungi, parasites.
Traps and rule of thumb
Trap: claiming a disinfectant 'sterilizes.' Trap: confusing a bloodborne pathogen with a fungus. Rule of thumb: if it cannot be disinfected (porous), it must be discarded after one client.