From the FDA Drug Label
Topical application of hydroquinone produces a reversible depigmentation of the skin by inhibition of the enzymatic oxidation of tyrosine to 3,4-dihydroxyphenylalanine (dopa) (Denton, C. et al., 1952)1 and suppression of other melanocyte metabolic processes (Jimbow, K. et al., 1974)2. The mechanism of action of hydroquinone (HQ) in treating hyperpigmentation is through:
- Inhibition of the enzymatic oxidation of tyrosine to 3,4-dihydroxyphenylalanine (dopa)
- Suppression of other melanocyte metabolic processes 1
From the Research
Hydroquinone treats hyperpigmentation primarily by inhibiting tyrosinase, the key enzyme in melanin production, as evidenced by the most recent study in 2024 2. When applied topically, hydroquinone penetrates the skin and interferes with the conversion of tyrosine to melanin in melanocytes, effectively reducing new pigment formation. Additionally, hydroquinone may cause selective damage to melanocytes and increase the degradation of melanosomes, further decreasing skin pigmentation. The mechanism of action of hydroquinone is supported by a study from 2021, which highlights its ability to competitively inhibit the enzyme tyrosinase 3. Another study from 2023 also confirms the effectiveness of hydroquinone in treating hyperpigmentation disorders, although it notes the importance of medical supervision due to potential side effects 4. Key points to consider when using hydroquinone for hyperpigmentation include:
- Typical treatment involves applying a 2-4% hydroquinone cream once or twice daily to affected areas for 8-12 weeks, followed by a maintenance period or break to prevent adverse effects.
- For optimal results, hydroquinone should be used with sun protection (SPF 30+) as UV exposure can worsen hyperpigmentation and reduce treatment efficacy.
- Side effects may include skin irritation, redness, and contact dermatitis, while prolonged use carries risks of exogenous ochronosis (paradoxical darkening) and permanent depigmentation.
- Due to these concerns, hydroquinone is often prescribed for short-term use under medical supervision, particularly at higher concentrations, as noted in a study from 2004 5 and further supported by the findings of a 1991 study on the mechanism of inhibition of melanogenesis by hydroquinone 6.