Ingredient Combinations

• Vitamin C + Vitamin E + Ferulic Acid: The gold-standard antioxidant combo. Ferulic acid stabilises and boosts both C and E. • Niacinamide + Retinol: Niacinamide reduces retinol irritation while both work on different ageing pathways. • Vitamin C + SPF: Vitamin C boosts SPF protection by up to 4x. • Hyaluronic Acid + Moisturiser: HA draws water in; moisturiser seals it. • Retinol + Peptides: Retinol stimulates collagen, peptides provide building blocks.

• Retinol + AHA/BHA: Alternate nights. Both are cell-turnover accelerators; using together causes irritation. • Vitamin C + Retinol: Vitamin C in AM, retinol in PM. Both are pH-sensitive and work best in different environments. • Benzoyl Peroxide + Retinol: Benzoyl peroxide degrades retinol. Use BP in AM, retinol in PM.

• Two retinoids together (retinol + tretinoin, retinol + adapalene) — excessive irritation, no added benefit. • AHA/BHA + Physical scrub on the same day — micro-tears and barrier damage. • Benzoyl peroxide + Vitamin C — BP oxidises Vitamin C, rendering it useless.

Vitamin C (L-ascorbic acid) needs pH < 3.5 to penetrate. AHAs/BHAs work at pH 3–4. Retinol works best at pH 5–6. Layering too many pH-sensitive products in one routine can reduce efficacy. Wait 10–15 minutes between different pH products.

Most active skincare ingredients are pH-sensitive. Layering them incorrectly can reduce their effectiveness. Key pH requirements: • Vitamin C (L-ascorbic acid): Effective at pH < 3.5 • AHAs (glycolic, lactic acid): Most effective at pH 3.0–4.0 • BHA (salicylic acid): Effective at pH 3.0–4.0 • Retinol: Works best at pH 5.0–6.5 • Niacinamide: Stable across pH 5–7 — the most compatible ingredient • Peptides: Most effective near physiological pH 6–7 What happens when you mismatch: If you apply niacinamide (pH ~6) immediately after vitamin C (pH ~3), the high-pH product temporarily raises the surface pH, reducing vitamin C's efficacy. Waiting 10–15 minutes allows the skin to return to its natural pH. Best practice — the 15-minute rule: Apply your lowest-pH product first (typically Vitamin C or AHA/BHA), wait 15 minutes, then proceed with the rest of your routine. Sequencing order (thinnest to thickest, lowest to highest pH): 1. Toner (if used) 2. Vitamin C or AHA/BHA — wait 15 minutes 3. Niacinamide or peptide serum 4. Hyaluronic acid 5. Moisturiser 6. SPF (AM only) or facial oil (PM)

Managing multiple actives across a week prevents over-exfoliation and maximises each ingredient's efficacy: Sunday: Rest day — just cleanser, moisturiser, SPF Monday AM: Vitamin C + SPF | PM: Retinol Tuesday AM: Vitamin C + SPF | PM: BHA exfoliant + niacinamide Wednesday AM: Vitamin C + SPF | PM: Retinol Thursday AM: Vitamin C + SPF | PM: Niacinamide + hyaluronic acid (no actives) Friday AM: Vitamin C + SPF | PM: Retinol Saturday AM: Vitamin C + SPF | PM: AHA mask + niacinamide Key principles: • Never retinol and AHA/BHA same night • Retinol maximum every other night initially • Vitamin C every morning is fine and recommended • One 'rest' day per week with no actives helps maintain a healthy barrier • If using benzoyl peroxide: AM only, ensure retinol is PM and vitamin C is separate step

Several widely circulated ingredient combination myths persist despite being disproven: Myth 1: Niacinamide + Vitamin C cancel each other out. Origin: a 1960s study found niacinamide and niacin (a different form of B3) form a yellow complex with ascorbic acid at high temperatures. Modern formulations at room temperature do not cause this reaction. Multiple studies confirm they are safe and even synergistic together. Myth 2: Retinol and vitamin C cannot be used in the same routine. They can — just not at the same step. Vitamin C in AM, retinol in PM. They address complementary anti-ageing pathways: C is your morning antioxidant shield, retinol is your night-time cellular repair signal. Myth 3: Peptides are deactivated by vitamin C. Some older research suggested acids could hydrolyse certain peptides. Modern research and formulation science indicate that topical peptides applied separately from low-pH vitamin C (with the 15-minute rule) remain intact and effective. Myth 4: You need a 30-minute wait between all layered products. The wait is specifically relevant for low-pH actives (vitamin C, AHA/BHA) before higher-pH layers. Other product-to-product waits of 30 minutes are unnecessary — just let each layer absorb before applying the next.