4-n-Butylresorcinol

Evidence by route

About this ingredient

4-n-Butylresorcinol (trade name Rucinol) is a synthetic resorcinol derivative. Among the most potent topical inhibitors of melanogenesis available in EU OTC cosmetics. Mechanism. Inhibits tyrosinase and the related TRP-1 protein – two key melanin synthesis enzymes. The dual action blocks melanogenesis more fully than arbutin or kojic acid. In vitro, 4-n-butylresorcinol is roughly 100-fold more potent than hydroquinone at tyrosinase inhibition (Khemis 2007). Where applied. Depigmenting serums and creams at 0.1–0.3%. In Spain: Sesderma Azelac Ru, Mesoestetic Cosmelan Hidra Ac Pro, Martiderm DSP-Bright. Often combined with retinol, niacinamide, azelaic acid, and vitamin C for additive effect. Evidence base. Khemis 2011 (n=28, 12 weeks, 0.3%) showed a 32% mMASI reduction in melasma – comparable to hydroquinone 4% but with lower irritation rate. Huh 2010 (n=23, 8 weeks, 0.1%) confirmed reduction of post-UV pigmentation. Safety. SCCS rated 4-n-butylresorcinol as acceptable at up to 0.3% in leave-on products (2018 opinion). Irritation and contact dermatitis occur in 3–8% of patients at initiation. Does not photosensitise. Pregnancy and lactation – use with caution. No direct pregnancy data; topical systemic absorption is low but non-zero, so avoid without necessity. Alternative for gestational melasma: azelaic acid 15–20% (pregnancy-approved) plus SPF 50+. Particularly suitable for. Persistent melasma, post-inflammatory hyperpigmentation after acne, lentigo. Not for sensitive skin or active rosacea.

Tolerability and safety

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