lead acetate. I worked in an environmental lab and one day all our water samples were spiking outrageously high in lead. As we began to check for contamination we traced it to my boss. He used Grecian Formula and had a habit of touching his hair. We were testing for ppm of lead at the time in waste water but this batch of samples was peeking out our equipment. Turns out Grecian Formula has %’s lead ! So just touching and equipment or glassware after touching his hair totally contaminated all the samples. So yeah, stay clear of that stuff unless you would like a measurable drop in IQ from nerve damage.

Seems like it no longer does in the US but it's incredibly frustrating that we wouldn't ban lead based ingredients more generally https://en.m.wikipedia.org/wiki/Grecian_Formula

I think I’ll stay away from lead.