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TONE + BRIGHTNESS
C Serum
TreatAMTone + Brightness
$75.00
C Serum
Tone + Brightness

C Serum

Daily vitamin C with ethyl ascorbic acid and niacinamide. Brightens tone, supports texture, and layers cleanly under hydration, oil, and SPF.

All Skin TypesAntioxidantTone + Brightness
$75.00 30 ml / 1 fl oz
100% PLASTIC-FREE
Formulated & shipped from Resonance Marin, Marin County, CA
Returns accepted within 30 days — half-full minimum
2-in-1
Ethyl ascorbic acid plus niacinamide for brightness and barrier support.
Dual
Water and oil solubility for improved compatibility and delivery.
Stable
Designed to stay active without the orange oxidation associated with traditional vitamin C.
100%
Plastic-free aluminum packaging, fully recyclable.
The Brief

Vitamin C that layers.
Brightness that lasts.

C Serum is the daily vitamin C treatment for tone, brightness, and texture. Designed for clients who wanted visible radiance without the sting of traditional vitamin C, it uses ethyl ascorbic acid in a lightweight formula that fits easily into a morning routine.

Read more

Ethyl ascorbic acid works alongside niacinamide to brighten dullness, refine uneven tone, and support a more resilient barrier. The water-light texture absorbs quickly under Hydrate Serum, Protect Oil, and Shield SPF 35+.

Result: skin looks smoother, clearer, and visibly brighter with consistent use.

The Brief
Where it fits
Where
it fits.
Morning.

C Serum is the daily vitamin C treatment in the Radiance System. Apply after XO Essence and before Hydrate Serum, Protect Oil, or SPF.

01
Cleanse
Gentle Cleanser
Preserves the barrier brightening depends on.

Apply first to remove SPF, makeup, and daily buildup without stripping. Brightening works best when the barrier is intact.

02
Activate
XO Essence
Prepares skin for vitamin C.

Apply to damp skin. XO Essence helps calm and prepare the skin so C Serum layers evenly.

03
Treat
C Serum
Daily ethyl ascorbic acid plus niacinamide.
You are here

Apply after XO Essence. Ethyl ascorbic acid supports visible brightness, while niacinamide helps refine tone and support barrier function.

04
Hydrate
Hydrate Serum
Supports even light reflection.

Apply after C Serum when the skin needs more water-binding hydration and comfort.

05
Finish
Protect Oil
Lipid vitamin C finish.

Apply after hydration when skin is stable and a lipid vitamin C finish is desired.

06
Protect
Shield SPF 35+
Final morning protection.

Apply as the final morning step. SPF protects the work your brightening routine supports.

Build Around This Step
Choose the next level of commitment: one product, a pair, a starter trio, or the full system.
Protect Oil Finish
Lipid Vitamin C
Protect Oil

The THD vitamin C finish after C Serum.

$85.00Discover
Radiance System Complete
Radiance System
Radiance System

The complete tone system: vitamin C, hydration, renewal, finish, and protection.

$434.00View System
2015
Vitamin C does not need to be aggressive to be effective. That was a marketing decision, not a chemistry one. Brightness is repetition.
— Daniella Inbar, Founder
The Science

Vitamin C that converts inside the skin. Stable on the outside, active where it counts.

01
Ethyl Ascorbic Acid / Vitamin C
A stable vitamin C derivative that converts into active vitamin C within the skin. It supports visible brightness, tone, and texture with better formula stability than traditional L-ascorbic acid.
02
Niacinamide / Vitamin B3
A barrier-supportive multitasker that helps refine uneven tone, improve the look of pores, and support skin resilience.
03
Licorice Root / Glabridin
A botanical brightening support known for helping reduce the look of uneven pigmentation while calming visible redness.
04
Propanediol / Plant-Derived
A plant-derived humectant that supports glide, hydration, and ingredient delivery while keeping the finish comfortable and non-sticky.
From the Treatment Room

Tips
from the spa.

Born in the spa, this formula reflects practitioner insight: clients needed a brightening serum that offered real results without irritation, something that could integrate seamlessly between treatments and support visible clarity week after week. C Serum was developed as this universal, daily antioxidant anchor.

Morning Antioxidant Layer
Layer C Serum beneath Shield SPF 35+ in the morning to support daytime radiance and antioxidant protection.
Brightness-Boosting Duo
Pair C Serum with Protect Oil when skin is stable and you want a multi-phase vitamin C routine. C Serum delivers the water-light treatment layer, while Protect Oil finishes with lipid-phase THD vitamin C.
After Mask Night
Use C Serum the morning after Radiance Mask, not directly over an exfoliating mask in the same routine. The mask helps refine surface texture, while C Serum helps maintain a brighter, more even look the next day.
The Details

Every question,
answered.

Formulated at Resonance Marin. Tested on real skin. These are the questions that matter most.

Where does C Serum fit in the system?
C Serum is the daily vitamin C treatment in the Radiance System. Use it after XO Essence and before Hydrate Serum, Protect Oil, and Shield SPF 35+.
What makes C Serum effective for brightness and uneven tone?
C Serum uses ethyl ascorbic acid, a stable vitamin C derivative, paired with niacinamide to support visible brightness, smoother texture, and a more even-looking tone.
How is ethyl ascorbic acid different from traditional vitamin C?
Ethyl ascorbic acid is a more stable vitamin C derivative that converts into active vitamin C within the skin. It is designed for better formula stability and daily compatibility.
Can I use C Serum with niacinamide?
Yes. C Serum already pairs ethyl ascorbic acid with niacinamide, so you get brightening and barrier support in one step. You do not need a separate niacinamide serum unless your routine specifically calls for one.
Can I use C Serum with Renew PM?
Most skin does best with C Serum in the morning and Renew PM in the evening. Separate them if you notice dryness, tightness, or redness.
Can I use C Serum with exfoliating acids?
Yes, but avoid over-layering actives. Keep C Serum in the morning and use exfoliating acids or Radiance Mask in the evening. Scale back if skin feels sensitive.
What makes INBAR+co C Serum different?
It combines a stable vitamin C derivative with niacinamide in a lightweight, layering-friendly texture designed for daily use under hydration, oil, and SPF.
Should I use C Serum morning or evening?
Morning is preferred for daily antioxidant support. It can also be used in the evening when your routine is simple, but always use SPF during the day.
Formula Feel
Antioxidant protection that disappears on contact.

A featherlight serum-gel that absorbs quickly and layers cleanly under hydration, oil, and SPF. The natural citrus aroma comes from essential oils, not synthetic fragrance, and dissipates after application.

CitrusTop
Natural Essential OilHeart
Featherlight GelHeart
No PillingTexture
Full Ingredient List
Every ingredient, listed.
Ethyl Ascorbic Acid, Niacinamide, Sodium Hyaluronate Crosspolymer, Sodium Hyaluronate, Sodium Acetylated Hyaluronate, Hydrolyzed Sodium Hyaluronate, Pentylene Glycol, Dimethicone, Polysilicone-11, Butylene Glycol, Decyl Glucoside, Polyacrylate-13, Polyisobutene, Polysorbate 20, Allantoin, D-Panthenol, Tocopherol, Lactic Acid, Glycyrrhiza Glabra (Licorice) Root Extract, Mica (CI 77019), Titanium Dioxide (CI 77891), Iron Oxide (CI 77491), Crystalline Silica, Phenoxyethanol, Ethylhexylglycerin, Parfum (Fragrance), Limonene, Linalool

Brighten. Layer. Repeat.

C Serum supports tone, brightness, and smoother-looking texture in a lightweight vitamin C layer built for morning use.

$75.00C Serum
View Radiance System →