Hydroquinone (HQ)

• Mechanism of action: hydroquinone inhibits activated tyrosinase activity (therefore it does not act on normal skin).

• A word on available concentrations:

1. 2%: often ineffective
2. 3-5%: good bleaching agent
3. 6-10%: higher concentrations can cause irritation

• Side effects:

1. Contact dermatitis (Both Allergic and Irritant)
2. Nail Discoloration
3. Exogenous Ochrnosis can rarely occur in dark skin individuals only (reports show exogenous ochronosis in Chinese patients of lighter skin types)

• How does Exogenous Ochronosis occur ?

1. Hydroquinone (HQ) inhibits homogentisic oxidase
2. This leads to the accumulation of homogentisic acid

• Dangers with Hydroquinone (HQ) usage:

1. Systemic absorption
2. Exogenous ochronosis
3. Carcinogenesis
4. Occupational Vitiligo

Bibliography: Katsambas A (Conflicts of Interest: Abbott, Janssen-Cilag, Leo Pharma, Merck, Schering-Plough). Melasma: Pathogenesis and Treatment. 70e Réunion annuelle de l’AAD (American Academy of Dermatology) – San Diego, California, United States of America (USA)

Source of information: here