Bleaching Creams. Common reactions to topical hyrdoquinone include contact dermatitis which is an allergic reaction, dryness, fissuring, erythema, burning, and irritation. Exogenous ochronosis, is a condition in which bluish black pigmentation of sun exposed skin has been seen after long term exposure to hydroquinone. Many doctors feel it should not be used more than 6 months.
Mercury. Some creams may contain mercury or other toxic substances.