Primary INCI Name: Ascorbic Acid
Vitamin C is a water-soluble antioxidant naturally found in the skin, where it supports collagen synthesis, protects against oxidative stress, and reduces hyperpigmentation [1]. While ascorbic acid is the purest form, its instability in formulations has led to the development of numerous derivatives with greater shelf life and skin compatibility [2].

Skincare Benefits

Evidence supports the following primary roles for vitamin C in topical formulations:

• Collagen synthesis: Topical application of vitamin C has been shown to increase collagen synthesis, stabilize collagen fibers, and decrease collagen degradation, contributing to its anti-aging effects [3].

• Antioxidant defense: vitamin C protects the skin from UV and pollution-induced oxidative stress [3].

• Reduction of hyperpigmentation: Vitamin C can inhibit tyrosinase, an enzyme involved in melanin production, leading to improved skin tone and fading of dark spots [1].

• Photoprotection: While not a sunscreen, vitamin C enhances the efficacy of UV filters and mitigates UV-induced skin damage when used in combination with SPF [4].

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Stability and Delivery Challenges

Ascorbic acid is unstable in aqueous solutions and rapidly oxidizes when exposed to air, light, or high temperatures. It also requires a low pH (~3.5) to remain active and penetrate the stratum corneum, which may be irritating to some users [5,6]. These limitations have led to the development of vitamin C derivatives that aim to improve stability, solubility, and skin compatibility.

Common Derivatives

Several derivatives are used in skincare, each with different chemical properties and levels of clinical evidence:

INCI Name	Solubility	Main distinction
Sodium Ascorbyl Phosphate (SAP)	Water-soluble	Studied for anti-acne effects
Magnesium Ascorbyl Phosphate (MAP)	Water-soluble	Gentler on skin
Ascorbyl Glucoside	Water-soluble	Gentler on skin
3-O-Ethyl Ascorbic Acid	Water-soluble	Good stability and penetration
Ascorbyl Palmitate	Oil-soluble	Low conversion
Ascorbyl Tetraisopalmitate	Oil-soluble	High stability; used in anti-aging
Tetrahexyldecyl Ascorbate (THD)	Oil-soluble	Highly penetrating
Sodium Ascorbate	Water-soluble	Gentler on skin

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Safety and Regulatory Status

Vitamin C and its derivatives are generally well-tolerated and widely used in cosmetic products. Ascorbic acid may cause stinging at high concentrations, especially on sensitive skin [7]. No major safety concerns exist for approved derivatives at standard concentrations in leave-on formulations.

Regulatory bodies such as the EU and FDA do not currently impose strict limits on vitamin C in cosmetics, though each derivative must comply with general safety regulations.

Conclusion

Vitamin C is a well-studied skincare ingredient with strong evidence for antioxidant, collagen-supporting, and brightening effects. While ascorbic acid is effective, its instability has led to the rise of more stable derivatives, each with unique properties. Choosing the right form depends on skin type, formulation goals, and clinical data supporting the specific derivative.

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References

1. Sanadi, R. M., & Deshmukh, R. S. (2020). The effect of Vitamin C on melanin pigmentation – A systematic review. Journal of Oral and Maxillofacial Pathology, 24(2), 374–382.
   https://pmc.ncbi.nlm.nih.gov/articles/PMC7802860/

2. Elhabak, M., Ibrahim, S., & Abouelatta, S. M. (2021). Topical delivery of l-ascorbic acid spanlastics for stability enhancement and treatment of UVB induced damaged skin. Drug Delivery, 28(1), 445–453.
   https://pmc.ncbi.nlm.nih.gov/articles/PMC7909477/

3. Al-Niaimi, F., & Chiang, N. Y. Z. (2017). Topical vitamin C and the skin: Mechanisms of action and clinical applications. The Journal of Clinical and Aesthetic Dermatology, 10(7), 14–17.
   https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5605218/

4. Jesus, A., Mota, S., Torres, A., Cruz, M. T., Sousa, E., Almeida, I. F., & Cidade, H. (2023). Antioxidants in sunscreens: Which and what for? Antioxidants, 12(1), 138.
   https://pmc.ncbi.nlm.nih.gov/articles/PMC9854756/

5. Kim, S., & Lee, T. G. (2018). Stabilization of L-ascorbic acid in cosmetic emulsions. Journal of Industrial and Engineering Chemistry, 57, 193–198.
   https://www.sciencedirect.com/science/article/abs/pii/S1226086X17304422

6. Martinović, L. S., et al (2023). Antioxidant activity, stability in aqueous medium and molecular docking/dynamics study of 6-amino- and N-methyl-6-amino-L-ascorbic acid. International Journal of Molecular Sciences, 24(2), 1410.
   https://www.mdpi.com/1422-0067/24/2/1410

7. Telang, P. S. (2013). Vitamin C in dermatology. Indian Dermatology Online Journal, 4(2), 143–146.
   https://pmc.ncbi.nlm.nih.gov/articles/PMC3673383/