I remember an episode of House (warning: spoilers!) in which a patient's psychotic break (and other subsequent life-threatening/organ failure-y symptoms, naturally) was traced back to excessive triclosan use, a common antibacterial agent found in clinical and laboratory hand soaps. In the episode, the patient was a pathologist who came into frequent contact on the job at the hospital, but over the years, triclosan and related derivatives have made their way into the household, commonly incorporated into all sorts of 'antibacterial' products from hand soaps, cleansers, mouthwashes and even plastic toys. It was suggested that 75% (back in 2008) of us excrete triclosan in our urine after absorbing this compound simply through normal daily contact.

Triclosan (and related triclocarban) is a an inhibitor of bacterial fatty acid synthesis (targeting FabI), though at high concentrations it is bactericidal via multiple mechanisms. With our successful push for greater hygiene to combat infectious disease transmission, triclosan has become a staple in soaps and washes in healthcare settings. It only seemed natural to move this into the home for general public use.

But doubts have lingered over triclosan's safety profile over the years since its introduction in the 1970s. Could this compound affect thyroid hormone levels or alter our microbiome to cause other pathologies? Well, some animal studies say yes, while other studies say no. A recent study in mSphere (an associated commentary) in human volunteers did not find any overt microbiome changes associated with triclosan use. But there are many variables--e.g., short term vs. long term exposure, dosage, ingestion vs. topical contact, size of cohort--that make it challenging to conclusively rule one way or the other on triclosan's impact on human health, and especially on the human microbiome (as is reviewed in a recent Science perspective).

But in addition to thinking about human safety, triclosan production and use means a significant introduction of these chemicals into the sewage system and environment, and there is concern that unintended impacts on natural bacterial communities can have adverse environmental effects or select for triclosan resistance (resistance mutants are readily isolated in the lab) that can be subsequently transferred to clinical strains. But again, not enough is known to conclusively point the finger in this regard, either.

So, the jury's still out on safety. But what about efficacy? Is it reasonable to use triclosan for benefits that outweigh the potential drawbacks? Well, in 2013, the FDA found that while triclosan use in toothpastes helped combat gingivitis, its inclusion in hand soaps had little benefit over other products. After reaching out to the companies to provide clinical data showing a clear benefit of triclosan over other hygiene products for bacterial burden or disease transmission, the FDA ruled last Friday that no such efficacy over standard soap and water washing could be convincingly demonstrated. Thus, given lingering safety concerns and unclear benefit to the general public, the FDA announced a ban on triclosan from over-the-counter (OTC) antibacterial washes. Companies have 1 year to remove triclosan and related compounds from OTC soaps and cleansers, but triclosan's use in health care settings remains permissible. Also unaffected are OTC alcohol-based 'sterilizers', and it is unclear how this ruling may impact triclosan use in other non-soap products.

The rise and fall of triclosan highlights the divide between the public perception that all microbes are unhygienic (and must therefore be eliminated) against data showing that these ideas are highly oversimplified and that the need for antimicrobials is largely context dependent. It also shows that we need greater vigilance and thought on how to appropriately use antimicrobials in general: while clinical overprescription and agricultural abuse have been major policy talking points, we've given relatively little thought to the consequences of other antimicrobial products in the everyday home environment, which arguably intersects with us more frequently.