Definition of phenolphthalein in English:



  • A colorless crystalline solid (pink in alkaline solution) used as an acid–base indicator and medicinally as a laxative.

    • ‘In fact, one popular laxative ingredient was taken off the market because scientists found ‘clear evidence of carcinogenic activity’ in laboratory animals exposed to phenolphthalein.’
    • ‘Bromthymol blue changes from yellow at pH 4 to blue around pH 7, and phenolphthalein changes from colorless at pH 7 to pink at pH 9.’
    • ‘The maintenance phase consisted of ‘Agarol’ (active ingredients: liquid paraffin, phenolphthalein, benzoic acid, and sorbic acid) 5-30 ml once or twice daily, senna granules, or bisacodyl tablets.’
    • ‘The listing is based on findings from feeding studies of phenolphthalein that caused cancer in multiple organs in multiple species of experimental animals.’
    • ‘The non-osmotic laxatives, phenolphthalein and senna, partly act by stimulating secretory mechanisms in the intestine.’


Late 19th century: from phenol + -phthal- (from naphthalene) + -in.