Ragwort poisoning through skin absorption. Fact or Fiction? Print E-mail
By Esther Hegt and Dr. Pieter B. Pelser ( University of Canterbury- Biological Sciences, Christchurch, New Zealand)

Several websites(1) and other media (2, (3) report that the poisons in ragwort (pyrrolizidine alkaloids) can be absorbed through the skin and therefore all skin contact with ragwort plants should be avoided. To find out if this information is accurate we went looking for the original source of this information. Up until now we have been able to trace these reports to two sources.

1) Paragraph 4.1.1 in a report from the World Health Organization in 1988 (4). Regarding absorption of pyrrolizidine alkaloids through the skin this report refers to an article written by Brauchli and colleagues (5). These scientists state that toxicological research on rats has proved that the pyrrolizidine alkaloids from the roots of comfrey (Symphytum officinale, Borganinaceae) can be absorbed through the skin. However, the amount of absorbed pyrrolizidine alkaloids appears to be much lower than when they where administered orally. The amount of pyrrolizidine alkaloids found in the urine of the rats was 20 to 50 times less than was measured when it was given orally. As long as the plant has not been eaten the pyrrolizidine alkaloids are in a N-oxide form and are not poisonous. When the plant is eaten they are transformed, mostly in the small intestine, into free alkaloids that are poisonous and that will damage the liver. The treatise of Brauchli and colleagues (1984) states that pyrrolizidine alkaloids that are absorbed through the skin are rarely, if ever, transformed into free alkaloids. We have not been able to find any more recent scientific studies on this subject.

2) Report on the internet by Dr. Knottenbelt (Liverpool University). This veterinarian is quoted on the internet quite a lot, because he stated, during a debate in the House of Commons, that the toxic substance in ragwort can almost certainly be absorbed through the skin (6). In response to this we contacted Dr. Knottenbelt. Through an email he informed us that there is no scientific proof for his statements. He writes that he himself has suffered liver damage after manually removing ragwort plants. The results of this ‘experiment’ have not been published and, according to us, are not obtained through a good scientific trial.

Through our research about the sources of the reports on the danger of touching ragwort, we conclude that there is no substantial evidence that there is a health risk for people. The amount of pyrrolizidine alkaloids that might be absorbed through the skin is very low and there is no proof that these alkaloids are being changed into a toxic form. Ragwort can cause an allergic skin reaction upon contact; compositae dermatitis (7). This allergy can appear after touching or eating the plant. This allergy is not caused by the pyrrolizidine alkaloids but by other substances that are common in many of the members of the Sunflower family (sesquiterpene lactones)(8).

(1) Ragwort-UK Ltd Educational site
(2) Yorkshire Dales Country News – 2006 Ragwort poisoning alert
(3) Nieuwsblad België-Jakobskruiskruid kan dodelijk zijn
(4) World Health Organisation. 1988. Environmental health criteria for Pyrrolizidine alkaloids. Published under the joint sponsorship of the United Nations Environment Programme and the World Health Organization. Geneva.
(5) Brauchli J., J. Luthy, U. Zweifel & C. Schlatter. 1982. Pyrrolizidine alkaloids from Symphytum officinale L. and their percutaneous absorption in rats. Experientia (Basel) 38: 1085-1087.
(6) Knottenbelt, D., House of Commons 25 Jul 2000 : Column 1089
(7) Gordon, L. A. 1999. Compositae dermatitis. Australas. J. Dermatol. 40: 123-128.
(8) Warshaw, E. M. & K. A Zug. 1996. Sesquiterpene lactone allergy. Am. J. Contact. Dermat. 7: 1-23