Question 1

What is the mechanism by which glycolic acid exfoliates the skin, and what pH range is required for it to be active?

Accepted Answer

Glycolic acid loosens the bonds between corneocytes in the stratum corneum by reducing calcium ion concentration, accelerating cell shedding. It must be formulated at a pH below 4.0 to remain in its free-acid, active form.

Question 2

Why is salicylic acid classified as a beta hydroxy acid particularly effective for acne-prone and oily skin types?

Accepted Answer

Salicylic acid is oil-soluble, allowing it to penetrate the lipid-rich environment inside sebaceous follicles, dissolve excess sebum, and loosen comedone plugs where water-soluble AHAs cannot reach effectively.

Question 3

What makes polyhydroxy acids (PHAs) such as gluconolactone gentler than AHAs, and for which skin condition are they particularly recommended?

Accepted Answer

PHAs have a larger molecular structure than AHAs, limiting their penetration depth and reducing irritation. They are recommended for rosacea and sensitive skin because they provide mild exfoliation without triggering significant erythema or stinging.

Question 4

Describe the conversion pathway of topical retinol to its active form in skin and the primary mechanism of its anti-aging effect.

Accepted Answer

Topical retinol is oxidized to retinaldehyde, then further oxidized to retinoic acid (tretinoin) within the skin. Retinoic acid binds nuclear receptors to accelerate keratinocyte cell turnover, stimulate collagen synthesis, and normalize follicular desquamation.

Question 5

What is the role of L-ascorbic acid in collagen synthesis, and what formulation pH is required to keep it stable and active?

Accepted Answer

L-ascorbic acid is a required cofactor for the enzymes prolyl and lysyl hydroxylase, which stabilize the triple-helix collagen structure. It must be formulated at a pH below 3.5 to remain in its bioavailable, active acid form and prevent rapid oxidation.

NIC Esthetics Exam — Cosmetic Chemistry & Ingredients

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