Quick Comparison
| Glycolic Acid | Vitamin C (L-Ascorbic Acid) | |
|---|---|---|
| Typical Concentration | Daily use: 5-10% at pH 3-4. Weekly peel: 10-30%. Professional peel: 30-70%. Start with 5% every other night. Increase concentration/frequency gradually. Always use SPF — AHAs increase sun sensitivity by up to 50%. Buffered formulations are gentler than free acid. | L-Ascorbic Acid: 10-20% at pH 2.5-3.5. Start with 10% if new to vitamin C. Apply in the morning under sunscreen for photoprotective synergy. The SkinCeuticals CE Ferulic formula (15% L-AA + 1% vitamin E + 0.5% ferulic acid) is the most studied and copied formulation. |
| Application | Topical (toner, serum, peel, cleanser). Leave-on products are more effective than wash-off. Apply to dry skin at night. | Topical (serum, usually water-based). Apply to clean, dry skin in the morning before sunscreen. Store in cool, dark place. Discard when it turns dark yellow or brown. |
| Research Papers | 9 papers | 10 papers |
| Categories |
Mechanism of Action
Glycolic Acid
Glycolic acid disrupts ionic bonds between corneocytes (dead skin cells) in the stratum corneum by chelating calcium ions and lowering the calcium concentration at desmosomal junctions. This weakens corneodesmosome integrity and activates endogenous proteases (kallikrein 5 and 7), accelerating desquamation. At higher concentrations, glycolic acid penetrates the viable epidermis and dermis, where it stimulates keratinocyte differentiation and upregulates transforming growth factor-beta (TGF-β) signaling in fibroblasts. This promotes glycosaminoglycan (GAG) synthesis, type I and III collagen production via procollagen gene expression, and elastin remodeling. Its small molecular size (76 Da) and high water solubility give it the deepest penetration of any AHA. The exfoliation also improves barrier function over time by promoting proper corneocyte maturation and reducing stratum corneum compaction.
Vitamin C (L-Ascorbic Acid)
L-Ascorbic acid donates electrons to scavenge reactive oxygen species (superoxide, hydroxyl radical, singlet oxygen) and reactive nitrogen species from UV, pollution, and metabolism—preventing oxidative damage to lipids, proteins, and DNA. It inhibits tyrosinase (copper enzyme catalyzing tyrosine to L-DOPA to dopaquinone) through copper chelation and competitive inhibition. Ascorbate is an essential cofactor for prolyl and lysyl hydroxylase—enzymes that hydroxylate collagen residues for triple-helix formation and lysyl oxidase crosslinking. Vitamin C regenerates oxidized vitamin E, creating a sustained redox cycle. Ferulic acid stabilizes both vitamins; the CE Ferulic combination provides 4-8x greater photoprotection than vitamin C alone. Penetration requires pH 2.5-3.5.
Risks & Safety
Glycolic Acid
Common
Stinging, redness, peeling, sun sensitivity. Over-exfoliation damages the skin barrier.
Serious
Chemical burns from professional-strength peels without proper protocol.
Rare
Scarring from improper high-concentration use.
Vitamin C (L-Ascorbic Acid)
Common
Tingling/stinging on application (due to low pH), oxidation of product (turns yellow/brown — discard when this happens).
Serious
None.
Rare
Contact dermatitis, especially with oxidized product. May cause temporary orange staining of skin at high concentrations.
Full Profiles
Glycolic Acid →
The smallest and most penetrating alpha-hydroxy acid (AHA). Derived from sugarcane, glycolic acid exfoliates by dissolving the bonds between dead skin cells on the surface, revealing smoother, brighter skin underneath. It is the most studied AHA with robust evidence for improving texture, fine lines, hyperpigmentation, and overall skin radiance. The gold standard chemical exfoliant.
Vitamin C (L-Ascorbic Acid) →
The most potent topical antioxidant with strong clinical evidence for brightening, anti-aging, and photoprotection. L-Ascorbic Acid is the pure, active form that directly neutralizes free radicals, inhibits melanin production, and stimulates collagen synthesis. The challenge is formulation — it is notoriously unstable and must be at low pH (2.5-3.5) for skin penetration, which can cause irritation.