Facts Frequently Misunderstood About Poison-Ivy

Note: Poison Ivy roots are common in unscreened topsoil, especially the black dirt often used in

                          Landscape beds.

             Birds also eat the fruit and help spread poison ivy to new areas in the landscape.

             Poison Ivy leaves can occasionally be shaped like oak leaves.

             The poison or resin can be active for many years on tools, lawn mowers, etc.

1. Poison-ivy is in the sumac family (Anacardiaceae) along with staghorn sumac and its close

 relatives: pistachio, cashew, mango, squawbush, poison-sumac, and some poisonous trees of the tropics.

 It is not closely related to Boston-ivy nor English-ivy.

2. Some poisonous relatives of poison-ivy are poison-sumac (Toxicodendron vernix), poison-wood

 (Metopium spp.), and guao or maiden-plum (Comocladia) of the Caribbean area, cashew (Anacardium

 occidentale), the dhobi-nut (Semecarpus), and the mango (Mangifera). In mango, the poison is in the

 pedicel and possibly in the "skin" of the fruit.

3. Poison-oak is not an oak, but a sumac. It is called poison-oak because its leaflets resemble the leaves

 of some native oaks.

4. There is no poison-oak in Michigan; elsewhere there are two species with this common name: one

 along the Pacific Coast (Toxicodendron diversilobum), and one in the southeastern United States

 (T. toxicarium).

5. There are two species of poison-ivy in the United States (and Canada, Mexico, and Western

 Guatemala and the Bahamas). One, which may grow as a shrub or vine is Toxicodendron radicans.

 There are a number of variants now recognized as subspecies. To the west of the 100th meridian of

 longitude and north of approximately the 44th parallel of latitude there is a non-climbing species,

T. rydbergii.

6. The chemical nature of the poison in poison-sumac or in either of the poison-oak species presumably

 is related chemically to that in poison-ivy, but its actual identity has yet to be determined. It is possible

 that the human body can detect differences between these poisons, but this has yet to be demonstrated.

 It is likely that a person who is "allergic" to one of these plants is allergic to them all.

7. The poisons are not volatile and, therefore, cannot be contracted "out of the air". A direct or

 secondary contact is necessary.

8. The poison may be spread in the smoke of burning poison-ivy because of tiny droplets of the poison

 present on the particles of dust and ash in the smoke.

9. Poison-ivy may be spread by animals. Petting a dog following his having run through a patch of the

 plant is a frequent way of contracting it.

10. Poison-ivy may be spread by articles of clothing. A person may reinfect himself by handling the

 same shoes he wore when he walked through a patch of the plant.

11. The poison cannot be spread by breaking the blisters on the skin.

12. There is little way of hastening the departure of the disease. Any medicines which are used on the

 skin serve to help dry the blisters, treat for secondary infection, or relieve itching. ACTH or cortisone

 derivatives will help cure the disease, but should be administered only with the advice and direction of a

 physician.

13. The level of sensitivity differs from person to person. Once one has surpassed his threshold of

 sensitivity, he will most likely alter that threshold. In some cases, it appears that a severe case will

 herald more severe cases; in others, it appears that one very virulent case precludes any others.

14. The initial contact is sufficient to give a person a rash if he is sufficiently sensitive. Normally,

 however, one must be sensitized by an initial contact before he will react by producing a rash.

15. Washing with strong soap merely removes excess poison from the skin, but will not remove any

 which has already reacted, because the poison is believed to form a complex with skin proteins. It is,

 therefore, not removable short of removing the skin! Even so, it is difficult to wash off this insoluble

 poison completely.

16. Injections are sporadic in effectiveness. They should generally be avoided as prophylactic measures,

 and definitely should be avoided during an attack of the dermatitis. At best, they may confer some

 degree of immunity; at worst, they may make a mildly sensitive person very sensitive.

17. Eating a leaf of poison-ivy may have disastrous results. One may surpass his normal level of

 immunity by the first bite; in this instance, he is headed for an internal case of poison-ivy, occasionally

 known to be fatal. The idea that American Indians chewed a leaf of poison-ivy to confer immunity is a

 myth which has never been documented.

18. The mechanism of sensitivity is not thoroughly understood. It does not behave like protein

 sensitivities such as hay fever pollenosis. It is hypersensitivity of the delayed type, whose mechanism is

 related to that of organ transplant rejection.

19. There are some persons who appear to be immune to poison-ivy. Probably very few persons are

 potentially totally immune, but rather have a) a high threshold of sensitivity or b) have never been

 sensitized. Any survey of the population generally reveals about 50% of those surveyed are immune at

 the time of census. Some studies seem to indicate that red-heads are more susceptible than blonds, who

 seem to be more sensitive than brunettes.

20. There is no known easy method for getting rid of poison-ivy, either the plant or the disease.

Prepared by William T. Gillis

September 1977

Dr. Gillis (now deceased) did his PhD Thesis on Poison Ivy with Dr. John Beaman in the Herbarium at

the MSU Department of Botany and Plant Pathology.