Dianthus Medical Blog Archive

Dettol protects: fact or fiction?

Posted on 14 Oct 2010 and filed under Pseudoscience Statistics 16 Comments

Readers in the UK (and possibly further afield, for all I know) will probably have seen a TV advert for a household disinfectant called Dettol, which has the strapline "Dettol protects: fact".

We are generally shown pictures of mummies with cute little kids and told how important it is to keep the kids protected, so the mummies clean their kitchens with Dettol. There is a clear implication that doing so will keep the little ones protected from nasty germs and therefore healthier.

There is a problem with that, however. Although I do not doubt for a minute that Dettol is highly effective in killing bacteria, to assume that killing a few bacteria around the kitchen translates into better health is a giant leap of faith. The fact is that bacteria are a normal part of our environment, and millions of years of evolution have equipped our immune systems to deal with them. Kitchens are not operating theatres. There is no obvious reason why it is necessary, or even desirable, for them to be sterile. Clearly, a bit of hygiene is sensible, and we don't want to leave chunks of rotting meat around, but going further than that and attempting to massacre bacteria at every opportunity doesn't have self-evident benefits.

But hang on a moment, I hear you cry, isn't it just obvious and common sense that fewer bacteria in your kitchen means a lower risk of infection? Well, no. As I said earlier, we are constantly exposed to bacteria in every part of our environment, and we have immune systems that are rather good at dealing with them. If we are to believe that wiping our kitchen surfaces with antibacterial products such as Dettol will improve our health, and if Dettol are going to make that claim in their adverts, then we need to see evidence that it is true.

So what does the evidence show?

OK, I haven't done the most thorough literature search in the whole world ever here, so it's possible I've missed something (and if I have, dear reader, do please let me know in the comments box below), but as far as I can tell, the evidence shows that household antibacterial products are not beneficial to health, and may possibly even be harmful.

Believe it or not, someone has actually done a randomised double-blind controlled trial of household antibacterial products, looking specifically at the rate of infections. They found that antibacterial products made no difference.

Concerns have also been raised that household antibacterial products may contribute not only to increased antibiotic resistance, but also, and I personally think this is a more important risk, to an increased risk of allergies.  The hygiene hypothesis, which is not yet conclusively proven, but which does have some pretty good evidence behind it, states that the immune system needs exposure to bacteria during childhood as part of the normal maturation process. If too few bacteria are encountered, the immune system has trouble figuring out what it is supposed to be doing, and develops allergic responses instead. This is widely believed (although I repeat, not completely proven) to be responsible for the huge increase in the prevalence of allergies in recent decades in developed countries, as standards of hygiene have improved and children encounter fewer bacteria.

Development of allergies is not a trivial matter. Food allergies can be fatal (although thankfully this is rare), but deaths from asthma, another disease with an allergic basis, are far more common. And that's on top of all the misery and discomfort from less serious allergies, such as eczema or hay fever.

To sum up, there is no evidence that Dettol protects against infections, and there is a prima facie case that it may increase the risk of allergies (although to my knowledge no-one has done a randomised controlled trial to look at the effect of Dettol on allergies, so we can't say with any certainty that it does).

Now, given that "Dettol protects: fact" seems to be such a misleading statement and utterly unsupported by evidence, I reported this advert to the Advertising Standards Authority. For those unfamiliar with it, this is a self-regulatory body in the UK, which is funded by the advertising industry, and claims to uphold standards among advertisers.

So, surely they wouldn't let such a misleading advert go unchallenged, would they? Well, yes, they would. They told me that other people have made complaints against Dettol in the past, and they have found in Dettol's favour, and so therefore they wouldn't consider my complaint. That would be fair enough if others had made the same complaint, but the other complaints were about completely different matters. For example, someone complained because they doubted the claim that Dettol could kill MRSA. Apparently it can, so it was fair enough that that complaint was not upheld.

That, however, is totally irrelevant to my complaint. I do not doubt that Dettol kills bacteria. My complaint was about Dettol's claim to protect human health, a claim for which there is, to the best of my knowledge, absolutely no evidence. In my humble opinion, it is irresponsible to advertise a product as being something that will protect your children's health, when in fact it may be harming them by increasing their risk of allergies.

That distinction was completely lost on the ASA. I see this as evidence that the conflict of interest that results from the ASA being funded by the advertising industry is not being well managed.

To sum up in advertising-speak:

Dettol protects: fiction. ASA protects advertisers: fact.

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