Skin Science
Skin Science
This domain tests the structure and function of skin, including the barrier, cell turnover, pigmentation, and the dermis. Questions often link product penetration and treatment choice to skin biology.
Core rules
- The epidermis has five layers in thick skin; the stratum corneum is the main barrier. The acid mantle is roughly pH 4.5-5.5 and supports barrier lipids and microbiome balance.
- Keratinocytes move upward and desquamate; turnover is often about 28 days in young adults and slows with age.
- Melanocytes produce melanin via melanogenesis; all skin types have similar melanocyte numbers, but production and distribution differ.
- The dermis contains collagen types I and III, elastin, glycosaminoglycans, fibroblasts, vessels, and nerves. Sebaceous glands produce sebum; eccrine glands produce sweat.
- Transepidermal water loss rises when barrier lipids are depleted, increasing irritation and penetration of actives.
Worked example
A client with dry, flaky skin asks for a strong AHA peel. Explain that flaking may reflect a compromised barrier, so aggressive exfoliation can increase penetration and irritation. Recommend gentle cleansing, barrier support, and a gradual exfoliation trial with patch testing. Reasoning: the stratum corneum controls penetration; barrier damage shifts dose-response and raises risk.
Traps
- Pores do not open and close; they can appear smaller when cleared.
- Blackheads are oxidized sebum and keratin, not dirt.
- Oily skin still needs hydration and barrier support.
- Melanocyte number is not the main determinant of skin color.