Jewelweed and Its Special Ingredient Lawsone – Poison Ivy Begone?

jewelweed
Jewelweed – Image by Fritz Geller-Grimm CC by SA 2.5
Orange jewelweed (Impatiens capensis)¹ commonly grows in ditches along roadsides at the edges of moist forests. Lore has it that the sap of this plant rubbed onto poison ivy rash quickly alleviates the itching.

Could there be a scientific basis for this popular notion? Perhaps. Let’s begin our consideration by discussing the active principle in both poison ivy and jewelweed.

Poison Ivy and Urushiol

Urushiol is not a single compound, but a mixture of similar compounds that have the generic chemical structure show in the image associated with this article. R represents an alkyl chain that typically contains 15 to 17 carbon atoms that contain varying numbers of double bonds. The greater the number of double bonds, typically the more virulent the urushiol fraction.

jewelweedUrushiol is a polar covalent compound. This means it and all its component parts are insoluble in water, yet can form hydrogen bonds.

Jewelweed and Lawsone

Lawsone is the principal and possibly active ingredient in jewelweed, and is a dye. Due to its prevalence in henna, it is also called hennatannic acid. Lawsone has been used in temporary tattoos and in dying hair, although its use is controlled, even forbidden in some nations. Hennatannic acid is a naphthoquinone derivative and, like urushiol, is a polar covalent species.

jewelweedCould It Be?

A general truism in chemistry is that like dissolves like. Urushiol and lawsone are both covalent, not ionic. They are both capable of forming hydrogen bonds. Could it be that lawsone in jewelweed sap, when applied to a fresh exposure of urushiol, hydrogen bonds to the urushiol and forms a kind of oily mix with it that can be partly wiped away? While it may not completely eliminate a rash from poison ivy exposure, might it not at least attenuate it so the sufferer gains some sense of relief?

¹ There is a yellow variety of jewelweed, Impatiens pallida.

Note: You might also enjoy Hydrogen Bonding Effects at Various Levels

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4 Comments

  • Exerciser Reply

    Interesting explanation. That might be something that a pharma firm would investigate. After all, if they could produce an item that could alleviate even part of the suffering from poison ivy, no doubt they would be able to make some money on that. It’s the kind of item that families would keep in a first aid box “just in case”.

  • Vincent Summers Reply

    Another thought concerning why jewelweed could cancel the effects of poison ivy are expressed in a book that says, “Dr. Rosen [a chemist at Rutgers University, New Brunswick says lawsone] binds to the same molecular site on the skin as urushiol. If applied quickly after contact with a poison plant, lawsone beats the urushiol to those sites, in effect locking it out. The simple result is that you don’t get the rash.”

  • Dan Lefever Reply

    I was just exploring this about jewelweed this week (have known of it for 40 years) while searching for information on the quinone component for use as a naturally occurring fungicide; which has been synthesized as a quinone based fungicide commercially. Mean while there were quite a lot of replicated studies referenced with jewelweed and poison ivy. Some showed little effect, others demonstrated a definite effect, but none showed any method that you could rely on being highly efficacious. Just google it if you want to explore it more.

    • Vincent Summers Reply

      I had heard what were, to me at the time, unproven rumors… wives’ tales. But the time arrived when the pro argument seemed to tip the scales the other way.

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