The possible carcinogen at question: formaldehyde.
Preservatives used in the shampoo release bits of formaldehyde. Johnson & Johnson said the preservative techniques are industry standard and they are safe and approved. Still, they do understand that parents have a new level of expectations, and for that reason, they have already begun changing the formulation in all countries. They also point consumers toward their Johnson’s Natural line, which is formaldehyde free, as an alternative.