Vitamin C serum for sensitive skin (typically in 30 ml bottles) is a concentrated liquid treatment designed to brighten the complexion and reduce dark spots without causing the irritation often associated with pure Vitamin C. For sensitive skin types, these serums often use stable derivatives like 3-O-Ethyl Ascorbic Acid or Sodium Ascorbyl Phosphate, which are gentler than pure L-Ascorbic Acid. 
Key Features for Sensitive Skin
Lower Concentrations: Experts recommend starting with 5–10% concentration to build tolerance safely.
Stable Derivatives: Use of forms like Ethyl Ascorbic Acid, which provide high Vitamin C content (~86%) at a skin-friendly pH (around 4.0–4.6) to prevent stinging.
Soothing Additives: Often formulated with Centella Asiatica, Hyaluronic Acid, or Vitamin E to maintain the skin barrier and provide hydration.
Fragrance-Free: Sensitive-skin formulas typically exclude dyes, mineral oils, and fragrances to minimize the risk of a reaction.
Usage Tips
Patch Test First: Apply a small amount to your inner forearm for 48–72 hours to check for redness.
Gradual Introduction: Start by using it every third day, then every other day, before moving to daily use.
Sun Protection: Always follow up with a broad-spectrum sunscreen in the morning, as Vitamin C can increase sun sensitivity while boosting SPF effectiveness.