Skin Anatomy, Physiology, and Histology
Skin anatomy, physiology, and histology questions test whether you can connect structure to treatment risk and product response. Expect layers, cell types, glands, barrier function, and wound healing.
Layers and cells
- Epidermis: avascular; from deep to surface: stratum basale, spinosum, granulosum, lucidum on palms and soles, corneum. Keratinocytes produce keratin; melanocytes in the basale make melanin; Langerhans cells are immune; Merkel cells are sensory.
- Dermis: papillary and reticular layers; collagen for strength, elastin for recoil; contains blood vessels, lymph, nerves, sebaceous glands, sweat glands, and hair follicles.
- Hypodermis: adipose and connective tissue; insulation, cushioning, and energy.
- Barrier: stratum corneum lipids and the acid mantle, about pH 4.5-5.5, limit water loss and microbial entry. Sebum and eccrine sweat contribute to the mantle.
Physiology
Eccrine glands are widespread and thermoregulatory; apocrine glands are in axillae and groin and become active at puberty. Sebaceous glands are largest on the face, scalp, and upper back. Inflammation and wound healing involve vasodilation, clotting, granulation, and remodeling.
Worked example
A client asks for a 'deep' exfoliation to 'reach the dermis.' Explain that cosmetic exfoliation acts on the epidermis; wounding the dermis is a medical procedure with scarring and infection risk. Choose a superficial option and patch test.
Traps
Placing melanocytes in the dermis; saying epidermis has blood vessels; confusing apocrine and eccrine distribution; assuming a thicker stratum corneum means a stronger barrier; promising dermal remodeling from a superficial product.