Vitamin C Guide: Benefits, Forms & How to Use It
Vitamin C is one of skincare’s most studied actives. This guide cuts through jargon to help you choose the right form, concentration, and routine—so you see real results, not just hype.
At a Glance (tl;dr)
- L-ascorbic acid (LA) is the benchmark; potent but can be irritating and unstable.
- Derivatives (THD ascorbate, MAP, SAP, AA glucoside, Ethyl AA) trade immediate potency for stability and tolerance.
- Sweet spot: 10–20% (LA or equivalent), paired with vitamin E + ferulic, in opaque/airless packaging.
- Use: AM or PM. If AM, always finish with broad-spectrum SPF.
Why Vitamin C Matters
Vitamin C provides antioxidant defence against UV-induced and pollution-driven free radicals, supports collagen synthesis, and helps even skin tone by interfering with tyrosinase activity. Consistency is key—expect visible gains in 8–12 weeks.
Forms of Vitamin C
L-Ascorbic Acid (LA)
The gold standard. Most potent evidence base; prefers low pH (<3.5). Can sting or cause transient redness in reactive skin.
Tetrahexyldecyl Ascorbate (THD)
Oil-soluble; penetrates lipid environments well. Great in richer serums/creams; typically gentler than LA.
Magnesium/Sodium Ascorbyl Phosphate (MAP/SAP)
Water-soluble, stable, and often better tolerated. Good starting point; pair with niacinamide or HA.
Ascorbyl Glucoside & Ethyl Ascorbic Acid
Stable, brightening-focused options that play nicely in multi-active routines.
What Strength Should You Use?
- Beginners / sensitive: 5–10% LA or derivatives
- Most users: 15–20% LA (or derivative equivalent)
- Above 20%: diminishing returns + higher irritation/instability risk
Packaging & Stability
- Choose opaque, airless containers to reduce oxidation.
- LA formulas work best at low pH; look for supporting antioxidants (E, ferulic).
- Store away from heat/light; refrigeration after opening can extend freshness.
How to Layer Vitamin C
- Cleanse → optional hydrating mist/toner.
- Apply vitamin C; wait ~30–60 seconds.
- Add humectants (e.g., HA) if desired.
- Seal with moisturiser appropriate to your skin type.
- AM only: finish with SPF 30–50+.
Using retinoids or strong acids? Alternate evenings to reduce irritation risk.
Common Myths & FAQs
Does higher % always work better?
Not necessarily. Above ~20% LA, irritation rises and benefit plateaus. Focus on formula quality and packaging.
Can I use vitamin C with niacinamide?
Yes in modern formulas. The “they cancel each other” myth is outdated. Many products combine them successfully.
Morning or evening?
Either. Morning pairs well with SPF for daytime defence; some prefer evening to minimise potential tingling.
How long before I see results?
Typically 8–12 weeks of consistent use for brightness and tone; collagen-related benefits accrue more gradually.
Need Help Choosing the Right Vitamin C?
Book a quick consultation and we’ll tailor strength, form, and layering to your skin type and lifestyle.