Chapter 30 — Quiz

Twenty-two questions. Answer without looking back at the chapter, then check. The answer key explains the reasoning, not just the letter, because in this chapter the reasoning is the point.

1. The stratum corneum consists principally of:

  • a) living keratinocytes in a collagen network
  • b) dead, keratin-filled corneocytes embedded in a lipid matrix
  • c) fibroblasts and elastin fibers
  • d) a single layer of tightly joined epithelial cells

2. The 500-dalton rule of thumb states that:

  • a) peptides below 500 daltons are biologically inactive
  • b) molecules above roughly 500 daltons penetrate intact skin poorly
  • c) cosmetic ingredients must legally be below 500 daltons
  • d) peptides above 500 daltons cannot be chemically synthesized

3. Which of the following is below the 500-dalton threshold?

  • a) acetyl hexapeptide-8
  • b) palmitoyl pentapeptide-4
  • c) GHK
  • d) botulinum toxin type A

4. The palmitoyl group on palmitoyl pentapeptide-4 was added primarily to:

  • a) increase the peptide's affinity for its fibroblast target
  • b) improve lipid solubility and therefore penetration
  • c) protect the peptide from proteases in the dermis
  • d) allow the molecule to be patented

5. Palmitoyl pentapeptide-4 is a fragment derived from:

  • a) elastin
  • b) SNAP-25
  • c) type I procollagen
  • d) lysyl oxidase

6. The proposed mechanism for signal peptides is that:

  • a) they physically fill in wrinkles from below
  • b) collagen breakdown fragments signal damage, prompting fibroblasts to synthesize new matrix
  • c) they inhibit matrix metalloproteinases directly
  • d) they deliver copper to lysyl oxidase

7. GHK is:

  • a) a synthetic hexapeptide first made in the 1990s
  • b) a naturally occurring tripeptide (glycyl-histidyl-lysine) that binds copper with high affinity
  • c) a fragment of type I procollagen
  • d) a botulinum toxin serotype

8. The central gap in the GHK-Cu evidence, as §30.4 describes it, is between:

  • a) animal studies and human studies
  • b) in-vitro and in-vivo work generally
  • c) a wound, where the barrier is already breached, and intact skin, where it is not
  • d) copper-complexed and free peptide forms

9. In Chapter 30, topical GHK-Cu for improving the appearance of aging skin is rated:

  • a) ✅ across the board
  • b) ❌ across the board
  • c) ⚠️ for modest instrument-measured effects; ❌ for the strong marketing version
  • d) 🔬, because it is too early to say

10. Acetyl hexapeptide-8 is derived from a portion of:

  • a) type I procollagen
  • b) SNAP-25
  • c) elastin
  • d) acetylcholinesterase

11. The SNARE complex is responsible for:

  • a) cross-linking collagen fibers
  • b) degrading extracellular matrix proteins
  • c) fusing neurotransmitter vesicles with the nerve terminal membrane
  • d) transporting copper into fibroblasts

12. The chapter rates topical acetyl hexapeptide-8, as an alternative to injected botulinum toxin, as ❌. The stated reason is:

  • a) the SNARE mechanism it invokes is fictitious
  • b) delivery, not mechanism
  • c) it is unsafe at cosmetic concentrations
  • d) no in-vitro data exists

13. Botulinum toxin type A produces muscle relaxation by:

  • a) competing with SNAP-25 for a place in the SNARE complex
  • b) cleaving SNAP-25 enzymatically, preventing acetylcholine release
  • c) blocking acetylcholine receptors on the muscle
  • d) depleting the nerve terminal of calcium

14. Approximately how large is the botulinum neurotoxin?

  • a) 890 daltons
  • b) 5,800 daltons
  • c) 150,000 daltons
  • d) 1,500,000 daltons

15. Which statement about botulinum toxin is correct?

  • a) Because it is naturally produced, it is inherently safer than synthetic alternatives
  • b) It carries a boxed warning about distant spread of toxin effect, and units are not interchangeable between products
  • c) It has cosmetic approvals but no approved medical indications
  • d) Its effects are permanent

16. In United States law, a product that claims to affect the structure or function of the body is:

  • a) a cosmetic
  • b) a cosmeceutical
  • c) a drug
  • d) a dietary supplement

17. The phrase "reduces the appearance of fine lines" is used because:

  • a) manufacturers are legally required to use that exact wording
  • b) a claim to actually change skin structure would make the product a drug requiring approval
  • c) it is more accurate than any alternative phrasing
  • d) it is a translation convention from European labeling

18. "Cosmeceutical" is best described as:

  • a) a third regulatory category between cosmetic and drug
  • b) a class of products requiring premarket safety review
  • c) an informal marketing term with no legal standing in the United States
  • d) the European term for an over-the-counter drug

19. The single most useful question to ask about a cosmetic efficacy study is:

  • a) how many participants were enrolled?
  • b) was it compared against the same formulation without the peptide?
  • c) was it published in a peer-reviewed journal?
  • d) how long did it run?

20. A cosmetic study compares an active serum against no treatment and reports improved corneometry and profilometry. The most likely explanation is:

  • a) the peptide reached dermal fibroblasts and stimulated collagen synthesis
  • b) the vehicle hydrated the stratum corneum, which improves both measures
  • c) the instruments were miscalibrated
  • d) regression to the mean fully accounts for both

21. A split-face design controls well for:

  • a) blinding of participants
  • b) between-person variation such as genetics, sun history, and season
  • c) carryover between treated areas
  • d) sponsor bias in reporting

22. According to §30.9, the intervention with the strongest evidence for slowing the visible aging of skin is:

  • a) topical copper peptides
  • b) daily sunscreen use
  • c) a peptide serum layered under a moisturizer
  • d) microneedling with a signal peptide
Answer key **1. (b)** Dead, keratin-filled corneocytes in a lipid matrix — the "bricks and mortar" arrangement. The living cells are below it, in the viable epidermis; the collagen and fibroblasts are below that, in the dermis. **2. (b)** It is a rule of thumb from the dermatology literature, not a law and not a regulation. Lipophilicity, charge, vehicle, and barrier integrity all modify it. Its practical use is as a prior: above 500 daltons, the burden of proof for penetration sits with whoever is claiming it. **3. (c)** GHK is around 340 daltons as the free tripeptide, with the copper complex not much heavier. Palmitoyl pentapeptide-4 is around 800 Da, acetyl hexapeptide-8 around 890 Da, and botulinum toxin around 150,000 Da. GHK's small size is a genuine point in its favor — and it establishes only that penetration is not ruled out, not that useful quantities reach fibroblasts. **4. (b)** Palmitoylation increases lipid solubility so the molecule partitions into the stratum corneum's lipid matrix. It is a delivery modification, not an activity one — the same chemical logic Chapter 33 describes for injected peptide drugs, aimed at a different obstacle. **5. (c)** Type I procollagen. The peptide is a subfragment of a propeptide region cleaved during collagen maturation. **6. (b)** Fragments of collagen breakdown are proposed to act as damage signals; applying the fragment counterfeits the signal. The mechanism is genuinely plausible and supported by real cell-culture work. (d) describes carrier peptides and (c) describes enzyme-inhibiting peptides. **7. (b)** Glycyl-histidyl-lysine, first isolated from human plasma in the early 1970s, binding copper with high affinity. **8. (c)** This is the chapter's central point about GHK-Cu. The wound-healing literature is real and decades old — and every result in it comes from a setting where the stratum corneum had already been cut, burned, abraded, or removed. Delivery was never the problem there. On intact skin it is. **9. (c)** The split rating, reproduced from Chapter 6 §6.8. One molecule, two claims, two ratings — Chapter 5's rule 6. A source giving GHK-Cu a single verdict has discarded the only distinction that matters. **10. (b)** SNAP-25, a component of the SNARE complex. **11. (c)** The SNARE complex zippers together to pull vesicle and terminal membranes into contact so neurotransmitter can be released. **12. (b)** Delivery. The mechanism it invokes is real — it is the same machinery botulinum toxin attacks. The failure is that the peptide must cross the stratum corneum, traverse the epidermis, cross a vascularized dermis that clears molecules away from the target, reach neuromuscular junctions in muscle, and arrive in bulk enough to compete with endogenous SNAP-25. Fractions multiply. **13. (b)** The light chain is a zinc-dependent protease that cleaves SNAP-25. This is catalytic: one toxin molecule destroys many substrate molecules — which is a materially different concentration requirement from the competitive mechanism proposed for acetyl hexapeptide-8. **14. (c)** Around 150,000 daltons — roughly 170 times the mass of acetyl hexapeptide-8, and utterly incapable of crossing intact skin. It works because it is injected. Route, not size. **15. (b)** Both parts are true and both matter. (a) is exactly the error Chapter 1 warns against: botulinum toxin is entirely natural and is one of the most potent biological toxins known. (c) is backwards — the medical approvals came first, in 1989, and the cosmetic use was noticed in the course of treating eye conditions. **16. (c)** A drug, by definition of intended use. A cosmetic may not make structure/function claims. **17. (b)** The vocabulary is a legal artifact. A claim to change skin structure converts the product into a drug requiring approval. Note the corollary in §30.7: a company that believed it could prove a structure/function claim would have every commercial incentive to make it. **18. (c)** No legal standing in the United States. A product is a cosmetic or a drug; there is no third box. **19. (b)** Because the vehicle is itself a moisturizer, and moisturized skin looks better and measures better. Without a matched vehicle arm, a study cannot separate the peptide from the base it is dissolved in. Sample size, journal, and duration all matter, but none of them rescues a study that lacks this comparison. **20. (b)** Hydrating the stratum corneum makes it swell, which pushes the walls of fine lines together and changes the mechanical and electrical properties the instruments measure. Every one of those changes is real. None of them requires an active ingredient. **21. (b)** Each participant is their own control, so genetics, sun exposure history, sleep, and season are matched perfectly. It does *not* solve blinding — if the preparations differ in feel, scent, or finish, participants often work out which is which, or believe they have — and it is vulnerable to carryover. **22. (b)** Daily sunscreen use, which has been tested in a randomized controlled trial with skin-aging endpoints over years. Nothing else in the chapter has evidence of that class for prevention. Saying so plainly is not a dismissal of the rest; it is the useful answer.