The Physics Police

The Physics Police

Wednesday, November 26, 2014

Chugging Triclosan Soap

A paper was published last week in the Proceedings of the National Academy of Sciences demonstrating that the commonly used antimicrobial additive triclosan is a liver tumor promoter. That's actually the title of the paper! Hilda Bastian at Scientific American wrote a good article on the study, calling out its authors on their hype and fear-mongering. She also points out the study's small sample size and that the positive results came at very high dosages.
... mice received less than 28.6 mg/kg TCS daily through water ... [1]
So, how much triclosan liquid soap would I have to drink daily in order to achieve this dose?

First, we need to know the concentration of triclosan in your average bottle of hand soap:
... most of the popular liquid hand soap brands contain between 0.1% and 0.45% weight/volume ... [2]
I'll be generous and assume that all of the 0.45% triclosan in our liquid soap is absorbed.

For your average 70 kg human the daily dose can now be calculated!

(70 kg) * (28.6 mg/kg) / (0.45%) = 445 g

Just shy of 16 oz. That's a lot of hand soap to use, much less drink. Daily.

You can't even bring that much on an airplane!
Unless you're actually drinking the stuff (don't), environmentally relevant doses from normal are measured in parts per billion [3, page 13], i.e. orders of magnitude lower concentrations than in this mouse liver study. In particular, absorption through the skin is very low, maybe 6.3% [3, page 11]. It's biological half-life is measured in hours [3, page 13].

Preventing antibacterial resistance is reason enough to avoid products with triclosan.

Argument from chemophobia isn't how we get people to use antimicrobial products responsibly.