The Skincare Ingredients Guide: What Retinol, Acids, Vitamin C and Peptides Really Do

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An ingredient list is a formula's blueprint. Once you know what each active does at the cellular level, you can choose products with intention, combine them intelligently and avoid the irritation that comes from layering the wrong things together. This guide covers the key families of cosmetic actives: retinoids, exfoliating acids, antioxidants, hydrators and barrier lipids, and peptides. It also explains which strengths are cosmetic and which require a prescription. It complements our Inside the Creams feature, which looks closely at niacinamide, copper peptides and panthenol.

Cosmetic or Prescription? Know the Line

In the United States, a product that changes the appearance of skin is regulated as a cosmetic. A product intended to treat a medical condition is regulated as a drug. Several of the best-known actives exist on both sides of that line.

• Retinol and retinaldehyde (retinal): cosmetic. Available over the counter in serums and creams.
• Tretinoin (retinoic acid): prescription only. It is a drug, not a cosmetic, and is prescribed for acne and photodamage (Mukherjee et al., 2006).
• Adapalene: the 0.1% gel became the first retinoid approved by the FDA for over-the-counter acne use in 2016. Higher strengths, such as 0.3%, and combination products remain prescription only (FDA, 2016).
• Tazarotene and trifarotene: prescription-only topical retinoids. Tazarotene carries a specific caution against use during pregnancy (DermNet).
• Hydroquinone: since the CARES Act took effect on September 23, 2020, over-the-counter skin-lightening products containing hydroquinone can no longer be legally sold in the US without FDA approval. In practice it is now obtained through a prescriber (FDA).
• Glycolic and lactic acid (AHAs): cosmetic at 10% or less with a final pH of 3.5 or higher, according to the Cosmetic Ingredient Review panel cited by the FDA (FDA, AHAs).

If you are considering any prescription active, speak with a board-certified dermatologist. Everything below refers to cosmetic-strength ingredients.

Retinoids: The Renewal Family

What does retinol do?

Retinol is a cosmetic form of vitamin A. Inside skin cells it is converted in two steps, retinol to retinaldehyde to retinoic acid. Retinoic acid binds nuclear retinoic acid receptors (RARs) that regulate gene expression. The result is faster keratinocyte turnover, support for collagen synthesis and reduced activity of the matrix metalloproteinases (MMPs) that degrade collagen (Mukherjee et al., 2006). On the surface, this helps improve the look of fine lines, rough texture and uneven tone over several months.

Retinal and bakuchiol

Retinaldehyde is one conversion step closer to retinoic acid, so it tends to act faster than retinol at the same strength. For sensitive skin, bakuchiol, a plant compound from Psoralea corylifolia seeds, is a popular alternative. In a 12-week randomized, double-blind study of 44 people, 0.5% bakuchiol twice daily and 0.5% retinol daily both significantly reduced wrinkle surface area and hyperpigmentation. The retinol group reported more scaling and stinging (Dhaliwal et al., 2019).

How to use: evenings only, a pea-sized amount on dry skin, two to three nights a week at first. Expect some dryness in the first weeks while skin adapts. Daily sunscreen is essential. Avoid retinoids during pregnancy and breastfeeding.

Exfoliating Acids: AHA and BHA

Glycolic acid (AHA)

Glycolic acid is the smallest alpha hydroxy acid, so it penetrates the stratum corneum readily. It loosens the corneodesmosomes, the protein "rivets" that hold dead surface cells together, so they shed evenly for brighter, smoother-looking skin. Research also describes effects deeper in the skin, including stimulation of collagen and hyaluronic acid production with repeated use (Tang & Yang, 2018). Lactic acid is a larger, gentler AHA and is also part of the skin's natural moisturizing factor.

Our Dermagenix GA-10 Facial Peel pairs glycolic acid (10%) with papaya enzymes, green tea and vitamins C and E, and is designed for once-weekly use at home.

Salicylic acid (BHA)

Salicylic acid is the principal beta hydroxy acid. Because it is oil-soluble, it moves into the sebum-filled pore lining, which makes it a favorite for oily skin and the look of congested pores. Over-the-counter acne products use it at 0.5–2%. Avoid it if you are allergic to aspirin.

Caution: AHAs increase sun sensitivity. The FDA recommends a "Sunburn Alert" on AHA cosmetics and advises using sunscreen while you use them (FDA, AHAs). Introduce acids slowly and don't use them on the same night as a retinoid until your skin tolerates both.

Antioxidants: Vitamin C, Vitamin E and Ferulic Acid

UV light and pollution generate reactive oxygen species (free radicals) that degrade collagen and lipids. Topical antioxidants help neutralize them.

• Vitamin C (L-ascorbic acid) is the best-studied topical antioxidant. It is an essential cofactor for the enzymes that stabilize collagen, and it inhibits tyrosinase, the enzyme behind melanin production. That is why it is associated with a brighter, more even-looking complexion (Al-Niaimi & Chiang, 2017).
• Vitamin E (tocopherol) is fat-soluble and protects cell-membrane lipids. Vitamin C helps regenerate it, so the two work as a team.
• Ferulic acid is a plant antioxidant. In a landmark laboratory study, adding 0.5% ferulic acid to 15% vitamin C and 1% vitamin E stabilized the formula and doubled its photoprotection of skin against simulated sunlight, from about 4-fold to about 8-fold (Lin et al., 2005).

Antioxidants complement sunscreen; they do not replace it. Use them in the morning under SPF. Our Dermagenix Revitalizer Anti-Aging Silk Cream combines vitamin C, vitamin E, niacinamide and a peptide complex.

Hydrators and the Barrier: Hyaluronic Acid vs. Ceramides

These two are often confused, but they do different jobs.

• Hyaluronic acid is a humectant, a glycosaminoglycan that binds water. The skin's own supply declines with age and sun exposure (Papakonstantinou et al., 2012). Applied topically, it draws moisture into the surface layers for a plumper, smoother look. Apply it to damp skin and seal it with a moisturizer.
• Ceramides are barrier lipids. Together with cholesterol and free fatty acids, they form the lamellar "mortar" between corneocytes that limits transepidermal water loss (TEWL). Correctly formulated ceramides support the look and feel of a healthy, resilient barrier (Schild et al., 2024).

In short, hyaluronic acid adds water and ceramides help keep it there. Our Dermagenix Intensive Recovery Eye Cream pairs both with nopal cactus and avocado extracts for the delicate eye contour.

Peptides: Cellular Messengers

Signal peptides

Signal peptides mimic fragments of broken-down collagen, which normally prompt fibroblasts to produce new matrix proteins. In a 12-week double-blind, placebo-controlled, split-face study of 93 women, a moisturizer with 3 ppm palmitoyl pentapeptide significantly improved the look of wrinkles and fine lines versus the same moisturizer without it (Robinson et al., 2005).

Acetyl hexapeptide-8 (Argireline)

This neuropeptide-inspired ingredient is designed to interfere with the SNARE protein complex involved in the signals that tell facial muscles to contract. An emulsion with 10% hexapeptide reduced wrinkle depth by up to 30% after 30 days (Blanes-Mira et al., 2002). A randomized, placebo-controlled trial of 60 people also found improvement in the look of lines around the eyes after four weeks (Wang et al., 2013). The studies are small, and the effect is far gentler than an injectable. You will find acetyl hexapeptide-8 in our Dermagenix Instant Eye Lift, and a related peptide, acetyl octapeptide-3, in our Dermagenix pH Balance Toner.

How to Layer Your Routine

Morning

1. Cleanse, then use a balancing toner.
2. Apply an antioxidant serum (vitamin C, E, ferulic).
3. Apply a hyaluronic acid serum to damp skin, followed by eye cream.
4. Apply a moisturizer with ceramides.
5. Finish with broad-spectrum SPF 30 or higher, every day.

Evening

1. Cleanse and tone.
2. Apply one "renewing" active per night: a retinoid or an AHA/BHA. Alternate them rather than stacking.
3. Apply peptides and hydrators.
4. Seal with a barrier-supporting moisturizer.

Pairings that work well: vitamin C with vitamin E and ferulic acid; retinoids with ceramides and hyaluronic acid; peptides with almost everything. Pairings to space out: retinoids with strong acids, and multiple exfoliants on the same night.

Cautions

• Introduce one new active at a time and patch test first.
• Retinoids and acids increase sun sensitivity, so sunscreen is non-negotiable.
• If you are pregnant or breastfeeding, avoid retinoids and ask your doctor about any active.
• If your skin stings, flakes or turns red, pause the actives and focus on barrier support.
• For persistent skin concerns, consult a board-certified dermatologist.

Frequently Asked Questions

What does retinol do for skin?

Skin cells convert retinol into retinoic acid, which regulates genes involved in cell turnover and collagen. Over months, it helps improve the look of fine lines, texture and uneven tone.

Hyaluronic acid vs. ceramides: which do I need?

Usually both. Hyaluronic acid is a humectant that attracts water; ceramides are lipids that help the barrier retain it.

Is tretinoin the same as retinol?

No. Tretinoin is retinoic acid itself and is a prescription drug. Retinol is a cosmetic precursor that skin must convert, so it is gentler and slower.

Can I use vitamin C and retinol together?

Yes, at different times of day. Vitamin C works well in the morning under sunscreen, and retinol belongs in the evening.

Is hydroquinone still available over the counter?

No. Since September 2020, OTC hydroquinone products cannot be legally marketed in the US without FDA approval. Ask a dermatologist about options.

Explore the Ingredients in Person

Our team at Gaia on Main is happy to walk you through any formula and help you build a routine around your skin. Visit us at 314 Main Street in Park City or 659 Sun Valley Road in Ketchum.

References

1. Mukherjee S, et al. Retinoids in the treatment of skin aging: an overview of clinical efficacy and safety. Clin Interv Aging. 2006;1(4):327–348. doi:10.2147/ciia.2006.1.4.327
2. U.S. FDA. FDA approves Differin Gel 0.1% for over-the-counter use to treat acne. July 8, 2016. fda.gov
3. DermNet. Topical retinoids. dermnetnz.org
4. U.S. FDA. FDA works to protect consumers from potentially harmful OTC skin lightening products (hydroquinone, CARES Act). fda.gov
5. U.S. FDA. Alpha hydroxy acids. fda.gov
6. Dhaliwal S, et al. Prospective, randomized, double-blind assessment of topical bakuchiol and retinol for facial photoageing. Br J Dermatol. 2019;180(2):289–296. doi:10.1111/bjd.16918
7. Tang SC, Yang JH. Dual effects of alpha-hydroxy acids on the skin. Molecules. 2018;23(4):863. doi:10.3390/molecules23040863
8. Al-Niaimi F, Chiang NYZ. Topical vitamin C and the skin: mechanisms of action and clinical applications. J Clin Aesthet Dermatol. 2017;10(7):14–17. PubMed 29104718
9. Lin FH, et al. Ferulic acid stabilizes a solution of vitamins C and E and doubles its photoprotection of skin. J Invest Dermatol. 2005;125(4):826–832. doi:10.1111/j.0022-202X.2005.23768.x
10. Papakonstantinou E, et al. Hyaluronic acid: a key molecule in skin aging. Dermatoendocrinol. 2012;4(3):253–258. doi:10.4161/derm.21923
11. Schild J, et al. The role of ceramides in skin barrier function and the importance of their correct formulation for skincare applications. Int J Cosmet Sci. 2024;46(4):526–543. doi:10.1111/ics.12972
12. Robinson LR, et al. Topical palmitoyl pentapeptide provides improvement in photoaged human facial skin. Int J Cosmet Sci. 2005;27(3):155–160. doi:10.1111/j.1467-2494.2005.00261.x
13. Blanes-Mira C, et al. A synthetic hexapeptide (Argireline) with antiwrinkle activity. Int J Cosmet Sci. 2002;24(5):303–310. doi:10.1046/j.1467-2494.2002.00153.x
14. Wang Y, et al. The anti-wrinkle efficacy of argireline, a synthetic hexapeptide, in Chinese subjects: a randomized, placebo-controlled study. Am J Clin Dermatol. 2013;14(2):147–153. doi:10.1007/s40257-013-0009-9

Disclaimer: This article is for educational purposes only and is not medical advice. Our products are cosmetics intended to improve the appearance of skin; they are not intended to diagnose, treat, cure or prevent any disease. The studies cited tested individual ingredients in their own formulations, not our products, and individual results vary. These statements have not been evaluated by the Food and Drug Administration. Patch test before first use and discontinue if irritation occurs.