An Open Letter to Stacy Malkan – The Dose Makes the Poison
I have noted that you make the claim that “we used to think that the dose makes the poison, but we now know that this isn’t true”. You are highly vocal in your efforts to sell your book and promote the “Campaign For Safe Cosmetics” and have used this claim in writing and in your presentations in the last couple of years, or so; manifesting itself in several slightly different ways, for example in this link, The Dose Makes the Poison? We Know Better Now.
As you know, “the dose makes the poison” is loosely taken from a quote from Paracelsus, the actual quote being “All substances are poisonous, there is none that is not a poison; the right dose differentiates a poison from a remedy.” This observation was made in the 16th century, and has remained a central tenet of toxicology since that time. Your observation that this is no longer true is incorrect, and I struggle to understand how you feel that there is any reason to claim this. The only explanation to which I can give any serious consideration is that you don’t understand the concept of “dose” in the manner in which is employed in toxicology. For simplicity, you can consider “dose” as being equivalent to “exposure”. Dose, or exposure, may be a single event, or it could be repeated ad infinitum. It remains a dose, and the dose, therefore, remains the poison.
You claim (in the link above):
Science has come a long way in that past five centuries [since Paracelsus]. Now we know: it’s not the dose that makes the poison, but also the timing of the dose, the size of the person and the toxicity of chemical mixtures — factors that aren’t considered in typical risk assessments.
This further compounds your lack of understanding of the meaning of “dose”. If you actually took the time to read a proper scientific study, you would see that the “dose” is always expressed in terms of weight of substance per kilo of bodyweight of the test subject per time period, e.g. 50mg/kg bodyweight/day. In other words, the dose means all the things you claim it doesn’t – quantity, timing AND the size of the person/subject species. (If a substance is suspected to have adverse effects during pregnancy, for example, it is generally tested at that stage in the test species, so the timing IS considered.)
Also, given that there are millions of chemical substances in existence, I am curious to know on what basis it would be decided which of the trillions upon trillions of different possible combinations should be tested in your quest to discover the toxicity of chemical mixtures. This is yet another example of the lack of understanding of the real world. If a particular combination of substances is suspected to be more toxic than the individual parts, for any specific reason, this could, and would, be tested.
I have no idea what constitutes a “typical risk assessment” in your world (that would be an interesting article to read), but I can give a typical risk assessment from the EU’s Scientific Committee for Consumer Safety (SCCS) that includes all of those things you say are omitted from these assessments – Clarification on Opinion SCCS/1348/10 in the light of the Danish clause of safeguard banning the use of parabens in cosmetic products intended for children under three years of age – all the studies considered in this extensive risk assessment quote the dose in terms of weight of substance per kilo of body weight of the test subject per time period.
This has not suddenly changed, and there is no “new thinking” as you attempt to suggest. Many toxicological studies are carried out on both a single dose basis and a repeat dose basis (to assess the effects of long term exposure), and have been for many decades. I hope that you will now stop claiming this as some wonderful new insight as it is simply not correct. Moreover, I trust that you will actually publish a retraction of your claim as it is clearly and totally incorrect, and serves only to mislead those who do not understand science.
More about the author: Dene Godfrey has been involved with preservatives for cosmetics since 1981, from both technical and commercial angles and has a degree in chemistry. Read more from this author