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Topical only. OTC cosmetic azelaic acid is typically around 10%; prescription strengths are 15% gel/foam (rosacea) and 20% cream (acne), applied as a thin layer to clean skin once or twice daily. There is no oral, injectable, or systemic dose. For rosacea or persistent acne, the prescription form under a clinician is the evidence-based route. This library does not provide an ingestion protocol.

Any time

Leave-on topical gel, foam, or cream (OTC ~10%, or prescription 15-20%)

Topical cosmetic only. L-ascorbic acid serums are typically 10-20% (often near pH 3 for absorption); stable derivatives are used at varying percentages. Apply a few drops to clean, dry skin, usually in the morning under sunscreen (its antioxidant action complements SPF). There is no oral, injectable, or systemic dose in this cosmetic context. This library does not provide an ingestion protocol.

Morning

Leave-on topical serum (10-20% L-ascorbic acid) or a stable vitamin C derivative

• For topical (skin) use only — not for ingestion, not for injection
• Known allergy or sensitivity to azelaic acid or formulation excipients
• Application to broken, severely irritated, or compromised skin until healed

• Other strong leave-on actives (retinoids, AHAs/BHAs, benzoyl peroxide)

• For topical (skin) use only — not for ingestion, not for injection (in this cosmetic context)
• Known allergy or sensitivity to the formulation
• Application to broken, irritated, or compromised skin until healed

• Strong leave-on actives (retinoids, AHAs/BHAs, benzoyl peroxide)
• Niacinamide