Senté Defense C Serum | 20% Stable Vitamin C with HSA

The two most common problems with Vitamin C serums are instability and irritation. L-Ascorbic Acid at 20% is highly effective but oxidises rapidly when exposed to air and light, and at concentrations above 15% can provoke significant irritation and redness in sensitive skin, particularly rosacea-prone and reactive skin types that would benefit most from Vitamin C antioxidant protection. Senté Defense C solves both problems simultaneously.

Formulated with 20% Tetrahexyldecyl Ascorbate, a highly stable, lipid-soluble form of Vitamin C that does not oxidise the same way as L-Ascorbic Acid in water-based formulas, and that penetrates through the lipid-rich epidermis more effectively because of its lipid solubility. Paired with Senté's patented HSA, the formula actively enhances tolerance and calms any inflammatory response rather than provoking it, making 20% Vitamin C activity appropriate for sensitive skin types that cannot tolerate standard high-concentration L-Ascorbic Acid serums.

Who Is It For?

• Sensitive, reactive and rosacea-prone skin wanting potent daily Vitamin C antioxidant protection without the irritation risk of standard high-concentration L-Ascorbic Acid
• Those who have had irritation or inflammatory reactions to previous Vitamin C serums
• Dull, pigmented or photodamaged skin wanting brightening and antioxidant protection in an HSA-containing formula
• Post-procedure skin cleared for serums where antioxidant support is a clinical priority
• Those on GLP-1 medications wanting maximum antioxidant protection in a sensitive-skin appropriate formula
• Those in the Senté programme wanting a Vitamin C serum step compatible with the HSA treatment products
• Menopausal skin wanting the benefits of high-concentration Vitamin C without irritation

How Does It Work?

Tetrahexyldecyl Ascorbate is a lipid-soluble ester of Vitamin C. Its lipid solubility allows it to penetrate through the epidermis's lipid-rich environment more effectively than water-soluble L-Ascorbic Acid, converting to Ascorbic Acid intracellularly where it is biologically active. Unlike L-Ascorbic Acid, it is stable in oil-based and mixed formulas without requiring the low pH conditions that L-Ascorbic Acid needs but that simultaneously increase irritation. At 20%, it provides maximum antioxidant free radical neutralisation, tyrosinase inhibition for brightening, collagen synthesis cofactor support and defence against UV, blue light and environmental oxidative damage. HSA actively modulates the inflammatory response at the site of application, making the formula genuinely appropriate for skin types that would normally react to 20% Vitamin C activity. The AOX antioxidant brightening blend adds Terminalia Chebula, Rice Bran, Sunflower, Rosemary extracts and Vitamin E for comprehensive environmental protection and brightening support.

Key Ingredients

• Tetrahexyldecyl Ascorbate (THD Ascorbate, 20%): Highly stable, lipid-soluble Vitamin C ester. Penetrates through the epidermis's lipid environment more effectively than L-Ascorbic Acid. Stable without low pH requirement. Converts intracellularly to active Ascorbic Acid. Provides maximum antioxidant protection, tyrosinase inhibition for brightening and collagen synthesis support at 20% concentration without the irritation risk of L-Ascorbic Acid at the same concentration.
• Heparan Sulfate Analog (HSA, patented, Senté): Actively modulates inflammatory signalling to enhance tolerance, calm any reactive response and strengthen the barrier. Works synergistically with THD Ascorbate to produce brightening and antioxidant results in sensitive and rosacea-prone skin types that would not tolerate a standard 20% Vitamin C serum.
• AOX Antioxidant Brightening Blend: Terminalia Chebula Fruit Extract, Rice Bran Extract, Sunflower Extract, Rosemary Extract and Vitamin E. Multi-source antioxidant protection against oxidative stress from UV, blue light, infrared and environmental pollution alongside the THD Ascorbate primary Vitamin C activity.

Benefits

• Stable 20% Vitamin C antioxidant protection without oxidation risk
• Brightens skin and reduces the appearance of dark spots and photodamage
• HSA calms inflammation and makes 20% Vitamin C tolerable for sensitive skin
• Supports collagen synthesis for firmer, more resilient skin
• Defends against UV, blue light, AGEs and environmental oxidative stress
• Lightweight, silky texture that absorbs quickly and layers easily
• Suitable for sensitive and reactive skin types that cannot tolerate standard high-concentration L-Ascorbic Acid

What Results Can You Expect?

At 4 weeks: improved skin radiance, early brightening and improved skin tone with consistent daily use. At 8 to 12 weeks: visible improvement in dark spots, photodamage and overall skin quality. Long-term: comprehensive antioxidant protection and cumulative brightening and collagen support.

How We Use It at Face for Soul

As a pharmacist prescriber specialising in skin health, Senté Defense C is the Vitamin C serum I recommend for patients who need potent daily antioxidant protection but have reactive or rosacea-prone skin that has not tolerated standard L-Ascorbic Acid serums. The THD Ascorbate stability and the HSA tolerance enhancement together solve the two problems that prevent sensitive skin patients from maintaining daily Vitamin C use. It is also the Vitamin C serum I recommend for post-procedure patients who need antioxidant protection but whose skin is not ready for the low-pH environment that L-Ascorbic Acid serums require.

How to Use

After cleansing, apply 1 to 2 pumps to the face and gently massage in morning and evening. Allow to fully absorb before applying moisturiser and SPF in the morning. In the Senté programme: use after the Daily Soothing Cleanser, apply Hydrate+ first if using both, then Defense C, then Dermal Repair Cream.

Frequently Asked Questions

Is THD Ascorbate as effective as L-Ascorbic Acid?
Yes, with advantages. THD Ascorbate converts intracellularly to active Ascorbic Acid, meaning the same biological activity operates inside the cell. Its lipid solubility provides better penetration through the epidermis's lipid environment. Its stability advantage means 20% THD Ascorbate in the bottle remains at 20% activity throughout the product's lifespan, whereas L-Ascorbic Acid at 20% begins oxidising from the moment it is manufactured.

Can I use it with tretinoin?
Yes. Apply in the morning with SPF. Apply tretinoin in the evening only. Do not use on the same evening.

Is it pregnancy safe?
No established pregnancy contraindications. Consult your midwife or obstetrician.

Is it suitable for rosacea-prone skin?
Yes, and this is one of its most significant clinical advantages. The HSA anti-inflammatory co-ingredient makes 20% Vitamin C activity tolerable for rosacea-prone skin that cannot use standard L-Ascorbic Acid at high concentrations.

Can I use it after procedures?
Once your clinician confirms serums can be reintroduced, Defense C is appropriate for post-procedure antioxidant support. Its tolerability in reactive skin makes it more appropriate for early post-procedure introduction than standard high-concentration L-Ascorbic Acid serums.

Does it clog pores?
No. Lightweight silky texture, non-comedogenic.

Is it cruelty-free?
Yes. Senté does not test on animals.

Clinical Insight

As a pharmacist prescriber, Defense C fills a specific clinical gap: maximum-strength Vitamin C antioxidant activity for patients whose reactive or rosacea-prone skin cannot tolerate standard L-Ascorbic Acid at high concentrations. The THD Ascorbate stability and the HSA tolerance enhancement together make daily 20% Vitamin C achievable for the skin types that need daily antioxidant protection most but have been previously unable to maintain it.

Research and Evidence

THD Ascorbate's lipid solubility, intracellular conversion to active Ascorbic Acid, and stability advantages over L-Ascorbic Acid are documented in published cosmetic chemistry research. Vitamin C's antioxidant, brightening and collagen synthesis mechanisms are among the most extensively published in dermatological literature. HSA's anti-inflammatory tolerance-enhancing mechanism is supported by Senté's clinical research and published Heparan Sulfate biology literature.

How Does It Compare?

Senté Defense C vs Obagi Professional-C Serum 20% (L-Ascorbic Acid): L-Ascorbic Acid at 20% requires low pH for stability and bioavailability, which increases irritation risk. THD Ascorbate at 20% is stable at neutral pH without low pH requirement and is genuinely appropriate for sensitive skin. Both provide 20% Vitamin C activity. Defense C is the appropriate choice for sensitive, rosacea-prone and reactive skin. Professional-C 20% is appropriate for normal to oily skin with established Vitamin C tolerance.

Senté Defense C vs NOON Antioxidant Complex: NOON uses multi-antioxidant approach including Vitamin C, E, Ferulic and Resveratrol. Defense C uses THD Ascorbate 20% plus AOX blend plus HSA. Different approaches to antioxidant protection. Defense C is the more targeted high-concentration Vitamin C option within an HSA-based programme.

Complete Your Routine

Morning: Senté Daily Soothing Cleanser, Senté Hydrate+ Serum (optional), Senté Defense C Serum, Senté Dermal Repair Cream, Senté Even Tone Mineral Sunscreen SPF 30. Evening: Senté Daily Soothing Cleanser, Senté Hydrate+ Serum (optional), Senté Dermal Repair Cream or Ultra Nourish.

Why Buy From Face for Soul?

At Face for Soul, Senté Defense C is the Vitamin C serum recommendation for patients with reactive or rosacea-prone skin who need daily antioxidant protection. As a prescriber managing patients who cannot maintain standard high-concentration L-Ascorbic Acid use due to sensitivity, the THD Ascorbate and HSA combination consistently makes daily Vitamin C achievable. Contact us before ordering if you have questions about whether Defense C or a standard Vitamin C serum is the appropriate choice for your skin.