Hydroquinone

What is Hydroquinone?

What hydroquinone is

Hydroquinone is a topical depigmenting agent used to treat hyperpigmentation conditions including melasma, post-inflammatory hyperpigmentation, freckles, and age spots. It’s available OTC at 2% concentration in some countries (banned OTC in the EU since 2001) and by prescription at 4% in the U.S.1.

It works by inhibiting tyrosinase, the enzyme that catalyzes melanin synthesis — effectively reducing the skin’s ability to produce new pigment.

Why hydroquinone is avoided in pregnancy

Hydroquinone has the highest systemic absorption of any topical cosmetic ingredient — studies have measured up to 35–45% absorption through intact skin, with detectable plasma levels2. By contrast, most topical actives absorb less than 5%.

This high absorption matters because:

• Once systemic, hydroquinone crosses the placenta.
• Animal studies have shown developmental toxicity at high doses.
• Pregnancy-specific safety data in humans are limited.

Although no clear association with birth defects has been documented, the asymmetric risk (cosmetic benefit vs. potential developmental harm) leads ACOG, the American Academy of Dermatology, and most national regulators to recommend avoidance in pregnancy3.

The melasma irony

Melasma — the “mask of pregnancy” — is one of the most common conditions for which hydroquinone is prescribed. Yet pregnancy is when it’s contraindicated. The good news: pregnancy-induced melasma often fades postpartum, and several pregnancy-safe alternatives can manage it in the meantime4.

Pregnancy-safe brightening alternatives

• Azelaic acid — Category B; effective for melasma and post-inflammatory hyperpigmentation.
• Niacinamide — reduces melanosome transfer; well-tolerated in pregnancy.
• Vitamin C (L-ascorbic acid) — antioxidant with brightening effect; pairs well with daytime mineral SPF.
• Daily mineral SPF — the most important melasma intervention; UV exposure worsens hyperpigmentation.