Hydroquinone

• Topical Depigmenting Agent
• Melasma: Lightening of hyperpigmented patches, particularly on the face
• Lentigines (age spots/sun spots): Treatment of localized hyperpigmentation
• Post-inflammatory Hyperpigmentation (PIH): Reduction of pigmentation following acne, eczema, or trauma
• Off-label / Clinically Accepted Uses
• Freckle reduction
• Certain cosmetic lightening regimens under dermatologist supervision

• Adults
• Apply 2–5% hydroquinone cream or gel to affected area once or twice daily
• Duration: 4–8 weeks, maximum 3–4 months continuously
• Pediatrics
• Limited data; use under strict medical supervision only
• Elderly
• Use standard adult dosing; monitor for skin sensitivity
• Application Instructions
• Clean and dry the affected area before application
• Apply a thin layer and gently rub in
• Avoid eyes, lips, and mucous membranes
• Combine with sunscreen for optimal results
• Special Populations
• Renal or hepatic impairment: No systemic absorption expected; standard topical dosing acceptable

Hydroquinone acts as a tyrosinase inhibitor, which is the key enzyme in melanin biosynthesis. By competitively inhibiting tyrosinase, hydroquinone prevents the conversion of tyrosine to DOPA and ultimately melanin, reducing pigmentation. The result is gradual lightening of hyperpigmented skin over several weeks of consistent application.

• Absorption: Minimal systemic absorption when used topically
• Distribution: Limited to epidermal layers; systemic distribution negligible
• Metabolism: Rapidly metabolized in the liver to hydroquinone glucuronide and sulfate conjugates if absorbed
• Excretion: Primarily via urine as conjugates
• Onset: Visible lightening may begin within 4–6 weeks of consistent use
• Duration of effect: Continued use required to maintain depigmentation; relapse may occur after discontinuation

• Pregnancy: No adequate well-controlled studies; generally not recommended during pregnancy due to theoretical risk of systemic absorption
• Lactation: Use with caution; avoid application to large skin areas, as safety data in breastfeeding infants are limited

• Primary Class: Dermatologic agent
• Subclass: Topical depigmenting / skin-lightening agent

• Known hypersensitivity to hydroquinone or any formulation excipients
• Erythematous, inflamed, or infected skin in the treatment area
• Patients with a history of ochronosis or chronic skin irritation

• High-risk patient groups: Dark-skinned individuals may be at higher risk of exogenous ochronosis
• Avoid prolonged use (>4 months continuously) to prevent skin ochronosis
• Monitor for contact dermatitis, burning, or irritation
• Limit sun exposure; always combine with broad-spectrum sunscreen
• Discontinue if severe irritation or hyperpigmentation occurs

• Common: Mild burning, stinging, redness, dryness
• Dermatologic: Erythema, itching, irritation, scaling
• Rare / Serious: Exogenous ochronosis (bluish-black pigmentation with chronic use), paradoxical hyperpigmentation, allergic contact dermatitis
• Timing: Usually within first 1–2 weeks of use, dose-dependent

• No major systemic drug interactions due to minimal absorption
• Topical corticosteroids or retinoids may enhance efficacy but increase irritation risk
• Avoid combining with strong oxidizing agents or chemical peels without dermatologic supervision

• Current dermatologic guidelines recommend short-term use (≤4 months) at ≤5% concentration
• Emphasize combination therapy with sunscreens for prevention of relapse
• Hydroquinone use restricted in some countries to prescription-only due to risk of ochronosis
• Alternative agents (e.g., kojic acid, azelaic acid) suggested for long-term maintenance

• Store at 20°C to 25°C (room temperature)
• Protect from light and moisture to prevent degradation
• Keep container tightly closed; do not freeze
• Avoid contamination; do not apply to open or infected wounds