Phenolphthalein (3,3-Bis(4-hydroxyphenyl)phthalide)

Manufactured for use as an acid–base indicator; formerly an active ingredient in stimulant laxatives and may still appear in some legacy or imported products [2].

Handling indicator powders/solutions at school or work (inhaling dust or skin contact) or ingesting medicines that contain it [2].

NTP lists phenolphthalein as “reasonably anticipated to be a human carcinogen,” and IARC classifies it as possibly carcinogenic to humans (Group 2B), based mainly on animal evidence and supporting mechanistic data [1][2].

Laboratory and manufacturing workers, and people using or handling old laxatives or chemical stocks without protection [1][2].

Check drug labels and avoid products listing phenolphthalein; choose alternatives. When handling in labs, minimize dust, use ventilation and PPE, wash hands, and clean work surfaces [1][2].