Plants are impeccable chemists and it is critical to understand the chemical traits of urushiol before discussing synthesis. This toxin is a mixture of alkyl catechols that is comprised of a 1,2 dihydroxybenzene ring (Flank, 1986). It is a phenolic compound, which means it consists of a benzene ring with a long hydrophobic side chain consisting of a large number of carbons on the carbon-3 position of the benzene ring, as shown in Figure 2. Depending of the specific plant containing urushiol, the amount of carbons in the side chain differs. While poison ivy and sumac have 15 carbons on its chain, poison oak has 17 carbons.
Urushiol is synthesized in the secretory cells of the resin ducts by the shikimic acid pathway. Resin components are derived from carbohydrates that are produced from photosynthesis. As shown from Figure 3, Protocatechuic acid is a product of the shikimic acid pathway and then used to produce urushiol (Caspi et al., 2013).
When discussing the amount or concentration of urushiol in plants, it does depend on the growth conditions and the particular season. A study performed by Japanese researchers indicated the percentage compositions of urushiol depending on its unsaturated bonds in Japanese, Korean, and Chinese Rhus vernicifera (lacquer trees). Researchers found that the most abundant urushiol was the triene urushiol at 71%, while the next most abundant was mono-urushiol at 14-16%, and diene urushiol at 5-8% concentration (Tetsuo et al., 2002).
Urushiol is vital to research and understand for a number of reasons. It is believed that urushiol’s purpose may be a defense mechanism for plants. When humans touch plants such as poison ivy are damaged, a skin dermatitis reaction due to urushiol results. Yet, it is interesting that while humans are allergic to urushiol, most other animals are not. Besides humans, only guinea pigs, rabbits, mice, and sheep have slight sensitivities to this toxin (Dickinson et al., 2013). Furthermore, it is also interesting to note that humans came late to North America, after poison ivy and urushiol were already present and prospering on the land, which also conflicts with this defense mechanism theory (Senchina, 2006).
There are several impacts urushiol has on humans and the environment -- both positive and negative. To start with harmful impacts on humans, there is the dermatitis reaction caused by urushiol when poison ivy tissue is damaged and it is released and in contact with humans. Some people are so sensitive to urushiol that only 2 micrograms on human skin can cause a reaction (Epstein et al., 1974). Around 80-90% of adult American individuals were reported to have a dermatitis rash when exposed to 50 micrograms of urushiol (Epstein et al, 1974). Additionally, urushiol can be difficult to wash off clothing and skin, so it can be spread by touching an urushiol-contaminated item. It is important to wash all skin and articles of clothing that may have come into contact right away to prevent the spread.