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Prescription topical. Hydroquinone is used at 2-4% (often as the triple-combination with a retinoid and a mild corticosteroid), applied to pigmented areas usually at night, in time-limited courses (commonly with treatment breaks) under clinician supervision, always with daily sunscreen. There is no oral or systemic use. Avoid indefinite continuous use because of ochronosis risk. This library does not provide an ingestion protocol.

Evening

Hydroquinone 2-4% cream or the triple-combination (with retinoid + mild steroid), under a clinician

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
• Prolonged continuous or high-strength use (ochronosis risk) — use time-limited courses
• Known allergy/sensitivity to hydroquinone

• Peroxides (benzoyl peroxide, hydrogen peroxide)
• Other irritating actives (retinoids, acids)

• 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