Skincare Active-Ingredient Harmony & Cult-Product INCI Directory

Unlike Tretinoin and Retinol, Adapalene’s rigid naphthoic acid structure resists Benzoyl Peroxide oxidation. However, layering both still doubles stratum corneum dryness.

Alpha-Arbutin is a glycosylated hydroquinone that remains stable at pH 4.5–6.5. Allow ultra-low-pH L-Ascorbic Acid (pH 2.8–3.2) to absorb for 10 minutes before layering Alpha-Arbutin.

Azelaic Acid (pH 4.9) and Niacinamide (pH 5.8) operate in adjacent physiological pH windows and synergistically calm PIE erythema, rosacea, and melanosome transfer.

Dermatologists frequently co-prescribe 15% Azelaic Acid with 0.05% Tretinoin for refractory melasma and acne. Their pH windows (4.9 vs 5.8) are compatible without redox degradation.

L-Ascorbic Acid and Azelaic Acid target hyperpigmentation via complementary pathways. Wait 10 minutes after low-pH Vitamin C before applying Azelaic Acid suspension/gel.

Bakuchiol stabilizes Retinol against singlet-oxygen degradation while calming retinoid-induced PGE2 and IL-8 inflammatory mediators.

Benzoyl Peroxide cleaves into oxygen free radicals that oxidize Tretinoin’s delicate polyene chain on contact, destroying >80% of retinoid potency within 2 hours while causing severe xerosis.

L-Ascorbic Acid is an electron donor; Benzoyl Peroxide is a strong peroxide oxidant. Applying them together causes immediate mutual neutralization on the skin surface.

Never layer Copper Tripeptide-1 (GHK-Cu) with L-Ascorbic Acid. Free and coordinated copper ions catalyze rapid oxidation of Vitamin C into dehydroascorbic acid while low pH (<3.5) strips copper from the tripeptide.

Pure L-Ascorbic Acid requires pH 2.6–3.4 to penetrate, whereas Retinol stabilizes at pH 5.5–6.5. Layering them in the same session creates a ΔpH 2.8 shock and spikes transepidermal water loss (TEWL).

Clinical trials demonstrate that combining Ascorbic Acid with Centella Asiatica triterpenoids (asiaticoside, madecassoside) multiplies fibroblast collagen synthesis while blunting low-pH stinging.

Glycolic Acid at pH 3.6 protonates the histidine nitrogen in GHK-Cu, breaking the copper coordination bond and hydrolyzing signal peptides.

While Copper Peptides and Retinol share a neutral pH window (~6.0), co-layering high-strength GHK-Cu with retinoids increases stinging and metal-catalyzed retinoid oxidation.

Salicylic Acid 2% (pH 3.5) destabilizes Copper Tripeptide-1 (pH 6.2) via a ΔpH 2.7 shift, releasing free copper ions that promote oxidative stress.

Gluconolactone (178 Da, pH 4.0) is far gentler than glycolic acid, but separating PHA to morning or alternate nights prevents retinoid sensitization.

Layering separate full-strength Glycolic Acid (7%) and Salicylic Acid (2%) leave-on toners dissolves both surface and follicular intercellular lipids simultaneously.

Hyaluronic Acid is 100% chemically compatible with Tretinoin, but applying Tretinoin onto wet HA-hydrated skin increases retinoid flux and stinging.

Combining Benzoyl Peroxide with Hydroquinone oxidizes hydroquinone into p-benzoquinone on the skin surface, causing dramatic dark brown/orange staining and acute irritation.

Hypochlorous Acid (HOCl) is a mild oxidizing antimicrobial. Spraying it directly onto wet L-Ascorbic Acid neutralizes both actives via rapid redox reaction.

Using a 1% Ketoconazole shampoo mask and leave-on Benzoyl Peroxide in the same session severely strips epidermal lipids and triggers rebound seborrhea.

Kojic Acid inhibits melanin exclusively by chelating copper ions at the active site of tyrosinase. Layering it with Copper Tripeptide-1 causes Kojic Acid to bind exogenous GHK-Cu instead, inactivating both.

Lactic Acid (pH 3.2–3.8) and Retinol (pH 6.0) overload epidermal turnover when layered on the same night, causing flaking and erythema.

Mandelic Acid (152 Da) penetrates slowly without triggering post-inflammatory hyperpigmentation in Fitzpatrick IV–VI skin. Wait 10 minutes before applying Niacinamide.

Strong Alpha Hydroxy Acids (pH 3.0–3.6) protonate and cleave delicate matrikine signal peptides (Palmitoyl Tripeptide-1 / Tetrapeptide-7), rendering expensive peptide serums inactive.

Applying pH 6.0 Niacinamide immediately over pH 3.6 Glycolic Acid buffers the acid’s un-ionized free-acid value and can trigger transient nicotinic acid conversion flushing in reactive skin.

Niacinamide (4%–5%) upregulates endogenous ceramide, free fatty acid, and cholesterol synthesis, clinically reducing Tretinoin-induced TEWL and peeling without lowering retinoid efficacy.

Niacinamide and Ascorbic Acid only form yellow nicotinic acid complexes under high heat, but layering pH 6.0 Niacinamide immediately over pH 3.0 LAA raises the acid pH and can flush reactive skin.

Salicylic Acid at pH 3.5 lowers skin surface pH, accelerating acid-catalyzed isomerization of retinol while compounding follicular desquamation.

Salicylic Acid (pH 3.5) and Azelaic Acid (pH 4.9) do not chemically deactivate one another, but layering both leave-on keratolytics in one session can over-strip sebaceous follicles.

While Salicylic Acid and Benzoyl Peroxide do not chemically deactivate each other, layering leave-on 2% BHA with 5.5% BPO strips sebaceous lipids and causes severe contact dermatitis.

Snail Secretion Filtrate (pH 6.5) provides allantoin, glycolic-bound glycoproteins, and panthenol that reduce Tretinoin flaking by 40%+ when allowed to dry before retinoid application.

Unlike L-Ascorbic Acid (pH 3.2), Tetrahexyldecyl Ascorbate is stable at pH 5.5–6.0, eliminating the ΔpH conflict with Retinol.

Tranexamic Acid (pH 5.6) and Tretinoin (pH 5.8) share the same physiological pH window and target hyperpigmentation without chemical antagonism.

L-Ascorbic Acid reduces oxidized dopaquinone while Tranexamic Acid blocks UV-induced plasmin signaling. Wait 10 minutes after low-pH Vitamin C before applying pH 5.6 Tranexamic Acid.

Stacking 7% Glycolic Acid (76 Da) beneath Rx Tretinoin strips the stratum corneum barrier, accelerates retinoid penetration into nerve endings, and triggers acute peeling.

At 5% concentration, Urea acts as a natural moisturizing factor and filaggrin upregulator that hydrates BHA-exfoliated pores without feeding Malassezia yeast.

Korean hospital-grade encapsulated ceramide-cholesterol-fatty acid barrier cream.

Sub-acidic pH 5.7 77% Heartleaf + Panthenol + Centella toner that neutralizes post-cleansing irritation.

Next-gen Korean UV filter emulsion with 30% Rice Extract + Niacinamide. Essential AM step to protect retinoid/acid routines.

Iconic pH 3.0 multi-acid (Lactic + PHA + BHA + Sulfur) resurfacing lotion. Extreme barrier hazard if combined with Tretinoin.

4% Niacinamide + 3 essential ceramides at pH 5.8. Contains Cetearyl Alcohol + Ceteareth-20 (watch for closed comedones in acne-prone skin).

96.3% Snail Secretion Filtrate + Panthenol + Allantoin buffer. Zero conflicts; ideal before retinoids.

Formulated by cosmetic chemist Joyce de Lemos with physiological ceramides, cholesterol, squalane, and urea.

Third-generation RAR-beta/gamma retinoid gel. Photostable and oxidation-resistant, but requires barrier lipid buffering.

25% multi-AHA + 2% Salicylic Acid peel at pH 3.5. Requires 48 hours of zero retinoids or other exfoliants.

Clinical 15% micronized Azelaic Acid hydrogel for rosacea, PIE, and melasma. Pregnancy Category B safe.

5% Panthenol + Madecassoside + Zinc barrier rescue balm for post-retinoid or post-peel recovery nights.

Micronized 5.5% Benzoyl Peroxide + 0.4% LHA. Potent oxidizer that chemically degrades Tretinoin, Retinol, and L-Ascorbic Acid on contact.

Engineered without C12-C24 fatty acids, esters, or polysorbates for strict Malassezia-safe barrier repair.

Cyclodextrin-encapsulated 0.06% Retinaldehyde serum. Separate from Benzoyl Peroxide and direct low-pH acids.

Cult pH 3.5 oil-soluble 2% Salicylic Acid desmolytic. Note: contains Polysorbate 20 (Malassezia trigger).

Prescription RAR nuclear agonist. Note: generic cream vehicle uses Isopropyl Myristate (Grade 5/5 comedogen).

Duke-patented pH 3.2 15% L-Ascorbic Acid + 1% Alpha-Tocopherol + 0.5% Ferulic Acid photoprotective gold standard.

Ultra-low pH 2.8 Lactic Acid treatment with high un-ionized free acid fraction. High ΔpH conflict with peptides and retinoids.

10-minute 30% AHA + 2% BHA rinse-off chemical peel. Never combine with any leave-on acid, retinoid, or benzoyl peroxide on the same night.

1% pure GHK-Cu + Matrixyl 3000 + Argireline at pH 6.2. Strictly incompatible with L-Ascorbic Acid, Glycolic Acid, and Salicylic Acid.

High-strength pH 3.6 low-molecular-weight AHA toner (3.6% free acid value). Causes severe barrier stripping if stacked with retinoids or copper peptides.

High-potency 20% L-Ascorbic Acid at pH 2.7. High ΔpH shock if layered immediately with peptides or niacinamide.

Multi-pathway tyrosinase & melanosome blocker combining Tranexamic Acid, Niacinamide, Azelaic Acid, and Kojic Acid.

0.015% Hypochlorous Acid antimicrobial mist. Wait 5-10 minutes to dry before applying Vitamin C or Peptides.