Numbuzin
No.5+ Vitamin-Niacinamide Concentrated Serum
Key ingredient: Vitamin Complex + Niacinamide
For users wanting the K-beauty 10% niacinamide standard alongside stabilised vitamin C derivatives in one bottle, the Numbuzin No.5+ Vitamin-Niacinamide Concentrated Serum debunks the old "you can't layer them" myth in formulation form — a single-product brightening stack at a price the equivalent Western combo can't match.
The ingredient story
Hero ingredient
Niacinamide 10% + Stabilised Vitamin C Derivatives
Concentration
10% niacinamide (the K-beauty standard) + 3-O-Ethyl Ascorbic Acid (oil-soluble, stable vitamin C derivative).
Deep-dive
Read the full guide →How it works
Niacinamide blocks melanosome transfer from melanocyte to keratinocyte (interrupting pigment delivery), regulates sebum output via SREBP-1 down-regulation, and supports the ceramide barrier. The 3-O-Ethyl Ascorbic Acid derivative is more pH-stable than L-ascorbic acid and inhibits tyrosinase (slowing pigment production at source). Together they hit hyperpigmentation from two complementary mechanisms — fewer melanosomes reaching the surface AND less melanin being made.
What the evidence shows
The myth that niacinamide and vitamin C "cancel each other out" comes from a 1960s study using extreme lab conditions (high temperature, pure ascorbic acid) that do not apply to cosmetic formulations. Modern multiple in-vivo studies show they retain efficacy together — see /ingredients/niacinamide for the full debunking.
Some users with very sensitive skin or rosacea-prone skin experience flushing at the 10% niacinamide concentration in the first 1–2 weeks. If that happens, dial back to alternate days, then build up.
The brand
Philosophy
“Numbered single-purpose products — each "No.X" is a focused stack targeting one specific outcome, no multi-active confusion.”
Numbuzin launched in 2021 as a Korean indie brand with a deliberately constrained product naming convention: every product is a number, and each number occupies a defined position in a routine (No.1 = first step, cleansing; No.3 = softening essence/serum; No.5 = brightening, etc.). This makes Numbuzin's catalogue genuinely scannable — you don't need to read marketing to know what each product is for. The brand grew rapidly in Korea through Olive Young and broke into Western markets via TikTok in 2023, with the No.3 Skin Softening Serum and No.5+ Vitamin-Niacinamide being the breakout products. Numbuzin is the contemporary K-beauty answer to the "10% niacinamide" category The Ordinary popularised — multi-active, stacked, well-formulated, and priced honestly (£15–25 range).
Where this fits in your routine
Routine step
Concentrated brightening serum — apply after toner/essence, before moisturiser
Morning: cleanse → toner → essence → No.5+ Serum → moisturiser → SPF (essential with brightening actives) Evening: double cleanse → toner → essence → No.5+ Serum OR retinol (alternate nights, don't stack both same night)
Introduction: Start every other day for the first 2 weeks if your skin is sensitive. The 10% niacinamide is the variable — most people tolerate it, but some experience a transient flushing or purging phase.
Pregnancy-safe.
Pairs especially well with
Beauty of Joseon Relief Sun SPF50+ — brightening actives require sunscreen to prevent re-pigmentation from UV — non-negotiable AM pairing
COSRX Snail 96 Mucin Power Essence — snail provides surface hydration that buffers any niacinamide tightness
Dr.Jart+ Ceramidin Cream — niacinamide upregulates ceramide synthesis; topical ceramides amplify the barrier effect
Full ingredients
Free from
Full INCI ingredient list (manufacturer)
Water, Niacinamide, Methylpropanediol, Glycerin, Butylene Glycol, 1,2-Hexanediol, Bifida Ferment Lysate, 3-O-Ethyl Ascorbic Acid, Pinus Sylvestris Leaf Extract, Saccharomyces Ferment Filtrate, Panthenol, Allantoin, Adenosine, Sodium Hyaluronate, Centella Asiatica Extract, Cetearyl Olivate, Sorbitan Olivate, Squalane, Carbomer, Tromethamine, Disodium EDTA, Tocopherol, Hydroxyacetophenone
What real users say
“My PIH (post-inflammatory hyperpigmentation) on my cheeks faded by about 70% in 10 weeks. No irritation, no purging — the gentlest brightening I have used that actually worked.”
— Reddit r/AsianBeauty, 2024
“I have rotated through 6 different niacinamide products and this is the only one I will repurchase. The vitamin C derivative addition genuinely makes a measurable difference.”
— TikTok review, @glowwithlydia
“For £18 you get a stack that would cost £50+ to assemble from The Ordinary single-actives. The K-beauty value-for-formulation calculus on this one is exceptional.”
— Cult Beauty verified review
Texture / feel
Lightweight, slightly milky serum that absorbs cleanly without tackiness. Faint herbal-clean scent (no added fragrance). Layers under sunscreen without pilling.
Buying authentic
Verified UK retailers
Counterfeit warning
Numbuzin uses a clean white-bottle design with a printed batch code on the base. Avoid Amazon UK marketplace third-party sellers — Numbuzin counterfeits have grown alongside the brand's Western popularity.
This page was last reviewed on 2026-05-19. We update product storytelling when formulation, retailer availability, or evidence changes meaningfully.
About this product
Bestselling vitamin serum to boost skin brightness and minimize pores. Lightweight gel texture absorbs fast for a glowing, energized complexion.
Why Vitamin Complex + Niacinamide works
Vitamin Complex + Niacinamide regulates sebum production, visibly minimises pores, and interrupts melanin transfer to fade dark spots.
Best for these skin types
Concerns addressed
BHA, niacinamide, and clay-based products help minimise pore appearance by controlling sebum.
