Hydroquinone toxicity

Short term and long term issues are described

Short-term: Exogenous ochronosis.

• It is a possible side effect from prolonged use of hydroquinone, especially at concentrations higher than 4%
• It has also been described for resorcinol, phenols (such as rhododenol), oral antimalarials.
• It is due to inhibition of homogentisic acid by hydroquinone.
• On histology, the following features are seen:
  • collagen degeneration
  • “banana-like” figures (intensely eosinophilic)
  • elastosis
  • pigment incontinence

Long-term: carcinogenicty

• In rats studies report a higher incidence of nephrogenic adenomas and soft cell tumors (leukemia)
• This effect has NOT been observed in humans
• As a precautionary measure, regulatory jurisdictions such as the European Union have been banned these agents in the “Over-the-counter” market and can only be prescribed by a doctor.

Source of information: Verma S. Hydroquinone revisited. European Academy of Dermatology and Venereology (EADV) Annual Meeting – Istanbul, Turkey, 2-6 October 2013