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J. Soc. Cosmet. Chem. 24 727-733 (1973) ¸ 1973 Society of Cosmetic Chemists of Great Britain Biological changes due to application of skin lightening compounds topical B. N. HEMSWORTH* Synopsis--Research has been reviewed relating to the use of SKIN LIGHTENING COM- POUNDS, their mode of ACTION and BIOLOGICAL EFFECTS. Knowledge of these changes is required for interpretation of ACUTE and LONG-TERM TOXICITY STUDIES involving mammalian species. Depigrnentation of black cats by hydroquinone was described by Ottel (1) and similar changes were reported in mice (2). The operative mechanism was considered to involve interference with pituitary function, a view supported by the work of Mishima and Chavin (3). However, hydro- quinone rapidly causes changes in pigment cells unlike the situation after hypophysectomy (4) suggesting a direct action on melanocytes and this may apply to the depigmentation of human skin (5). The effect of hydro- quinone on skin is limited in range and transient, and incorporation of this compound in preparations to the 3•o level does not cause sensitivity, but in higher dosage (5•o level) patients become sensitized. Patch tests are positive and lesions said to vary from acrokeratosis verruciformis to almost an anaplastic condition. A perivascular infiltrate generally accompanies skin lightening and although the number of melanocytes appears normal the quantity of melanin is virtually halved. Response of negro skin to hydroquinone seems to depend on the amount of pigment, for only in lighter skin can a response be observed. Changes in skin colour can be due * Life Sciences Laboratory, Polytechnic, Teesside, Middlesbrough, England. 727