Hydroquinone

Tolerability and safety

Working concentrations

2–4% (prescription in most countries)

Irritation potential

Medium

Allergen risk

Moderate

Pregnancy

Avoid

Suitable for

Normal, Combination, Oily

Use with caution

Sensitive, Dry

For sensitive skin

Prolonged use (>6 months) without breaks can cause ochronosis – irreversible skin darkening. Used in 3–4 month cycles with rest periods.

About this ingredient

Hydroquinone is the strongest topical depigmenting agent in dermatology, used since the 1960s. Produced synthetically. Mechanism. Competitively inhibits tyrosinase – the key enzyme of melanin synthesis. Also cytotoxic to melanocytes: oxidizes to benzoquinone, which damages melanocyte membranes and mitochondria. Reduces melanin synthesis and the number of active melanocytes in the treated area. Where applied. Pharmaceutical 2-4%, in specialized compounding – up to 10%. Standard of care for melasma, post-inflammatory hyperpigmentation, lentigines. Often in the Kligman formula (hydroquinone 4% + tretinoin 0.05% + dexamethasone 0.01%) for severe melasma. In Spain – prescription only (Pranagen, Crema Despigmentante, Kligman formula via compounding pharmacies). In the US 2% forms were OTC until 2020, then the FDA removed them from OTC over ochronosis risk and safety concerns. Evidence base. Numerous RCTs since the 1970s confirmed efficacy in melasma (Ennes 2000, Espinal-Perez 2004 meta-analysis), MASI-score reduction 30-50% over 8-12 weeks. Outperforms most alternatives (azelaic acid, kojic acid, arbutin). Combination with tretinoin and steroid yields a higher effect. Controversy and ochronosis. Long-term use (>6-12 months) of high concentrations (>4%) causes exogenous ochronosis – gray-blue skin discoloration from homogentisic acid accumulation in the dermis. More common in darker skin. Cases are rare but irreversible. EU SCCS rates hydroquinone as Cat. 2 carcinogen for systemic use, but topical dermatological concentrations are not banned (prescription). In cosmetics EU Regulation 1223/2009 permits hydroquinone only in hair dyes ≤0.3% and artificial nails ≤0.02% – banned in skin creams. Safety. Irritation, erythema, peeling – frequent. Persistent hypo- or hyperpigmentation with improper use. Courses of 3-6 months with breaks are recommended. Pregnancy – contraindicated (FDA category C). 4-6% systemic absorption is described in pregnant patients. Lactation – contraindicated. Alternatives: tranexamic acid (topical and oral), azelaic acid, cysteamine.

Frequently asked questions