Personal care products disrupt the human oxidation field

"the human health impacts of many such chemicals remain poorly understood"

The effects of ritual bathing (soap, scrubbing with washcloths, etc.) on the skin may also be "poorly understood". Many people also wear regularly-washed clothing.

When I look at the laundry-list of chemicals in personal-care products (soaps, shampoos) (and in foods ... sometimes, wow!) I often wonder how much effort goes into testing all of this gunk.

Occasionally when I shower I get this vivid vision: a man comes home from hard days work and takes a shower. Grabs his shampoo but only squirts out half of his usual amount because shampoo bottle is empty, he thinks it will be enough but after applying it instantly feels it's not enough, so he grabs his wife's shampoo, squirts the second half and rubs it onto his hair. Few seconds later his hair bursts into fire because different chemicals in two completely different shampoos reacted together. How plausible is this scenario?

I don't think it's very plausible for shampoo but it's relevant for toothpaste for sensitive teeth. There's are two mechanisms for sensitive teeth, one is to flood the nerve with potassium ions using potassium nitrate, i.e. saltpetre. The other method is to block access to the nerve endings with other chemicals. You could potentially mix toothpaste and get your mouth to warm up slightly.