Compare Products: The Niacinamide 15 Serum vs 20% Vitamin C + E Ferulic Acid Serum

COSRX

The Niacinamide 15 Serum

Mid-range15%
$25 / 20ml — $1.25/ml

Who It's Designed For

COSRX
  • Oily and acne-prone skin seeking serious oil control
  • Post-acne marks and hyperpigmentation
  • Enlarged pores and textured skin
  • Users ready to step up from 10% to higher-strength niacinamide
  • Those who prefer minimal-ingredient formulas
Timeless
  • Those seeking the CE Ferulic combination at an affordable price
  • Users comfortable with high-concentration L-ascorbic acid
  • People looking for a research-backed antioxidant serum
  • Budget-conscious shoppers who want SkinCeuticals-level actives
  • Users who prefer fragrance-free, minimalist formulas

Key Ingredients

COSRX

Niacinamide (15%), Acetyl Glucosamine (2%), Zinc PCA (1%), Allantoin (0.1%)

Timeless

20% L-Ascorbic Acid, 1% Vitamin E (Alpha Tocopherol), 1% Ferulic Acid, Sodium Hyaluronate, Panthenol

Product Composition

13% similarity (3 ingredients in common)

Shared Ingredients
watersodium phytatetocopherol
Only in COSRX (13)
pentylene glycolniacinamidebutylene glycolacetyl glucosamine12-hexanediolzinc pcatrehalosexanthan gumpullulanallantoinethylhexylglycerincitric acid
Only in Timeless (8)
ethoxydiglycoll-ascorbic acidpropylene glycolpolysorbate 80panthenolferulic acidbenzyl alcoholdehydroacetic acid

User Feedback Patterns

COSRX
Oil control standout

Users consistently report significant reduction in daytime oil and shine. Many describe it as the best niacinamide serum they have tried for sebum control.

Lightweight texture praised

Unlike some high-concentration serums, this absorbs quickly without tackiness or residue. Layers well under other products.

Small bottle concern

The 20ml size (vs. 30ml standard) is a common gripe, especially given the price point.

Pore improvement takes time

Users report visible pore improvement around the 3-4 week mark with consistent twice-daily use.

Timeless
Effective and affordable CE Ferulic

The most common praise is that it delivers results comparable to SkinCeuticals at a fraction of the cost. Users report brightening, improved tone, and visible glow within 2-4 weeks.

Reddit favorite

Consistently ranked among the top vitamin C serums on Reddit. r/SkincareAddiction and r/30PlusSkinCare frequently recommend it as the best value CE Ferulic serum.

Oxidation is the main complaint

Users report the serum darkening within 4-8 weeks, sometimes faster in warm climates. Several recommend buying smaller sizes and refrigerating immediately.

Stinging on initial use

The 20% concentration causes noticeable stinging for most users during the first 1-2 weeks. This typically subsides as skin adjusts.

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