Name: Dr Koo Anti-Oxidant Vitamin Serum | THD Vitamin C
Brand: Dr. Koo Skin Care
Price: 200.00 USD
Availability: InStock

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Lipid-Soluble Dermal Delivery: THD-Ascorbate crosses the stratum corneum and is activated intracellularly by esterases — delivering the required cofactor for prolyl hydroxylase directly at the fibroblast level, where collagen synthesis actually occurs. Unlike conventional water-soluble Vitamin C, this formula reaches the dermis
Therapeutic Concentration: Every active dosed at the concentration that reaches the fibroblast in an amount the cell can use — not the minimum required to print on a label. 15% THD-Ascorbate, stated outright, balanced to deliver results without overloading the skin
Collagen Synthesis Support: Provides continuous ascorbate cofactor for prolyl hydroxylase — the enzyme that hydroxylates proline residues in procollagen for stable collagen triple-helix formation. Two applications daily maintain the cofactor pool through the full 24-hour collagen synthesis cycle
Multi-Vitamin Antioxidant Complex: Vitamins C, D, E, F, and K work synergistically with ceramides, jojoba, and marula oil to reinforce the lipid barrier, regulate melanocyte activity, and provide comprehensive antioxidant defense
Post-Procedure Compatible: Formulated by a plastic surgeon for use on surgical and post-treatment skin. No harsh acids. No barrier-stripping chemicals. Every ingredient earns its place without damaging the tissue it is designed to improve — the mechanism behind plastic surgeon's personal recommendation

Morning Protocol

Step 1 — Cleanse. Start with clean, dry skin. THD-Ascorbate is lipid-soluble — it crosses the stratum corneum most efficiently when the surface is free of residual product and sebum.

Step 2 — Apply 3-4 drops. Press the formula into the skin — do not rub. The lipid-soluble ester needs sustained contact with the stratum corneum to begin transdermal delivery.

Step 3 — Wait 60 seconds before layering. Allow the serum to absorb before applying moisturizer and SPF. This absorption window gives THD-Ascorbate time to begin crossing the lipid barrier before the next layer seals the surface.

Evening Protocol

Repeat after evening cleansing. Collagen synthesis is not a once-a-day event. Prolyl hydroxylase — the enzyme that drives collagen formation — requires a continuous supply of ascorbate cofactor. A single morning application depletes by mid-afternoon. Evening application replenishes the cofactor pool overnight, when cell turnover and repair activity peak.

The 60-Second Rule

Apply within 2 minutes of cleansing, while the stratum corneum is still slightly warm and the lipid matrix is most permeable. Wait 60 seconds after application before layering anything on top. This gives the full therapeutic dose time to begin reaching the target tissue.

What to Expect

Week 1-2: Actives begin saturating target skin layers. Subtle texture and clarity shift as the formula establishes dermal presence.

Week 2-4: Fibroblasts respond with increased collagen production. One full melanin cycle completes — pigment begins to normalize. Brightening becomes visible.

Month 2-3: Two full collagen remodeling cycles complete. Visible firmness improvement. Fine lines begin to soften as new collagen architecture forms.

Month 3+: Sustained collagen support compounds — not a surface effect, but a change in how skin behaves under stress: faster recovery, less reactivity, better tolerance of actives.

WHAT IT IS

A surgeon-formulated vitamin serum built on THD-Ascorbate (Tetrahexyldecyl Ascorbate) — the lipid-soluble form of Vitamin C that crosses the stratum corneum and is activated intracellularly by esterases at the fibroblast level, where collagen is actually synthesized.

Unlike conventional water-soluble Vitamin C that oxidizes on the skin surface, THD-Ascorbate reaches the dermis intact and delivers the required cofactor for prolyl hydroxylase — the enzyme responsible for stable collagen triple-helix formation.

Five vitamins at therapeutic concentration, each earning its place through mechanism, not marketing:

✔️ Vitamin C (THD-Ascorbate) — collagen synthesis cofactor at the fibroblast level

✔️ Vitamin D — supports cellular differentiation and skin barrier integrity

✔️ Vitamin E — lipid-soluble antioxidant that stabilizes cell membranes

✔️ Vitamin F — essential fatty acids that reinforce the lipid barrier

✔️ Vitamin K — supports microcirculation and reduces vascular discoloration

Why the Serum Comes First

Retinol signals the fibroblast to build collagen. Ascorbate is the cofactor the fibroblast requires to finish it. The serum goes on first, the retinol layers on top.

A published histological study of a topical retinol–vitamin C combination found it partially reversed the changes of both chronological aging and photoaging in treated skin.

Seité S, et al. Skin Pharmacol Physiol. 2005;18(2):81–87.

THD-Ascorbate Vitamin C Serum bottle by Dr. Koo — stable lipid-soluble formula stays clear and active

FORMULATION INTEGRITY

Stable to the Last Drop

Most Vitamin C serums use L-ascorbic acid — which oxidizes within weeks of opening. You can see it: the formula turns brown.

THD-Ascorbate is inherently stable. It remains clear and active from the first pump to the last, delivering consistent therapeutic potency throughout the life of the bottle.

Vitamin C Serum Comparison

	Dr. Koo Vitamin C Serum	SkinCeuticals C E Ferulic	La Mer Revitalizing Serum	Dr. Barbara Sturm The Good C	Augustinus Bader The Serum
Plastic Surgeon Formulated	✓	—	—	—	—
Contains THD-Ascorbate	✓	—	—	✓	—
Contains Vitamin F	✓	—	—	✓	✓
Contains Vitamin K	✓	—	—	—	—
Contains Marula Oil	✓	—	—	—	—
Price (USD)	$200	$182	$270	$180	$200

Comparison based on publicly available product information and ingredient lists.

SOOOO MORE THAN 5 STARS

“OMG. I can feel it. Love it. My skin craves it. Medical grade. Ingredients in purest forms. My skin loves it. And this makes me love my skin.”

- Margaret D.

FOUNTAIN OF YOUTH!

“This product may seem expensive but when I think of how much money I have wasted over the years to find a product that is simple and so effective it is worth the extra cost. This is the fountain of youth!”

- Tara N.

BEST SERUM I'VE USED

“After just a few weeks of use, I'd never received more out-of-the-blue compliments on how well I looked!”

- Kevin

FAQ

Can I use this with retinol?

Yes — and in fact, they work better together.
This antioxidant serum is designed to enhance the performance of retinol, not compete with it. Its lipid-soluble antioxidants help calm inflammation, support the skin barrier, and reduce oxidative stress, which can otherwise limit how well retinol is tolerated.
Used together, the serum helps soothe and stabilize the skin, allowing retinol to do its collagen-stimulating work more effectively and with less irritation over time.
Why this formula is different: Antioxidants are selected to calm inflammation and support the barrier, allowing retinol to work more effectively with less irritation.

How does this serum fit into a complete skincare protocol?

This serum is designed as the active treatment step in both your morning and evening protocol. In the morning, apply after cleansing and before moisturizer and SPF — THD-Ascorbate provides antioxidant defense against UV-generated free radicals throughout the day. In the evening, apply before your retinol — the lipid-soluble antioxidants help calm inflammation and support the skin barrier, allowing retinol to work more effectively with less irritation. The two products are synergistic, not competing.

How long until I see results?

You may notice improved brightness and clarity within the first few weeks. More meaningful improvements in tone, texture, and overall skin quality typically appear with consistent twice daily use over 8–12 weeks, aligning with normal skin turnover and collagen remodeling.
Why this formula is different: Clinically meaningful concentrations work within the skin cycle to improve skin quality, not just surface appearance.

Why does THD-Ascorbate penetrate differently than regular Vitamin C?

Because THD ascorbate is lipid-soluble, it penetrates more effectively and remains stable longer than traditional vitamin C forms, helping deliver antioxidant support where repair happens.

Dr Koo Anti-Oxidant Vitamin Serum | THD Vitamin C

WHAT IT IS

Why the Serum Comes First

FORMULATION INTEGRITY

Stable to the Last Drop

Vitamin C Serum Comparison

WHAT EVERYONE’S SAYING

FAQ

Customer Reviews