|What causes poison oak to irritate the skin? What
does that have to do with chemistry?
|Question Date: 2010-01-11|
Poison oak is a member of the Anacardiaceae -
the Cashew Family. The family has many members
that cause skin irritations, including (for many
people) the cashew plant itself and the mango. In
all cases the irritant is an oil that is borne in
the outer conducting tissue of the plant - its
phloem. Phloem as a tissue is composed of several
cell types. One of these is a secretaory cell that
generates the irritating substance, which is then
carried within the surficial layers of the plant
in laticifers, anastomosing canals. When one
breaks the skin one releases the irritating
The active substance is Urushiol.
Here I refer you to the excellent summation at
does it have to do with Chemistry? Well, on the
one hand, the plant is synthesizing urushiol (a
chemical) from hydrogen, oxygen and water (see the
complex diagrams at Wikipedia) so it is acting as
a natural chemist. Further, it is by the study of
its composition that human chemists can understand
the composition of urushiol and potentially
suggest ways to reduce its irritating properties.
Finally, it is by biochemistry that we can
understand how urushiol creates the irritation
that it does in many, but not all, humans.
Yes, this can be a burning question, so to
speak.Poison oak contains an oil called urushiol.
Urushiol triggers a reaction from your immune
system called an inflammatory response. Your
immune system protects you from germs and
parasites. But some things that are not germs or
parasites can also trigger a response from the
immune system. That's what an allergy is, a big
immune system response to something that would be
important because the shapes of molecules make
them more or less likely to trigger an immune
response. Antibodies have particular shapes that
bind with other molecules. Some shapes are more
likely to fit antibodies than others are. You
could develop an allergy to almost anything, but
some things are particularly likely to cause an
allergy. You may know a few people who are at
least a little allergic to peanuts or cats. You
probably don't know anyone allergic to apples or
glass. About 90% of people will have an
inflammation reaction to the urushiol in poison
Why do you think some plants make
urushiol? How would it benefit the plant
Thanks for asking,
Poison oak contains a chemical called urushiol
that is produced in the leaves, branches, roots
and flowers of poison oak (scientific name
Toxicodendron diversiloba). The rash is caused
due to the bodys immune system trying to fight the
poisonous oil. The oils can be transferred
directly from the plant or can be present on your
clothes, your dog, etc and then transfer to you.
The chemical urushiol is what causes the
irritation from poison oak, poison ivy and sumac.
It is found in their leaves, stems and roots and
has this chemical structure:Urushiol
the group that says "R" can be any one of the
following:R = (CH2)14CH3
The chemical (usually a mixture
of several above) penetrates and binds to your
skin cells. The long carbon chains of the R
groups cause the chemical to bind very tightly
making it difficult to wash off. Once the
compound is bound to your skin cells your body
sees those cells as dangerous causing an immune
response. The itching redness and rash is the
result of your body trying to destroy the cells
the urushiol is bound to.
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