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1
Click on the pictures (in
number order) below to
learn more about the
urushiols’ effect on
humans.
2
What causes the
symptoms?
Who gets it?
Poison ivy
Poison oak
3
Who gets it?
About 50% of people
will get poison ivy
or poison oak when
they brush up
against a plant in
nature.
Does age matter?
In one study urushiol containing leaves were
rubbed on the backs of individuals of
various ages, and the following was found.
What occupations get it?
It affects those who spend
significant time in the
forest the most. For
example 10% of the days
taken off by lumberjacks
is due to urushiol
allergies, and 1/3 of
forest firefighters have
gotten poison oak or
poison ivy by inhaling
urushiols during a fire.
What causes the symptoms?
When urushiols are transferred to the skin,
they will remain there for 3 days if not
washed off.
Because urushiols are small lipophilic
molecules they can easily penetrate the
epidermis of the skin or the layers of the
respiratory tract and cause a delayed type
hypersensitivity reaction (DTH). The next
three slides illustrate the 3 steps of these
reactions.
Afferent Phase
•
•
•
Because urushiols are lipophilic they are able to
pass through the membrane of the Langerhan
cells (LC) in the epidermis of the skin.
The urushiols are displayed on the surface of the
cell by an MHC I molecule.
Some of the LC cells
then travel to the
lymph nodes (see picture)
where T cells will be
activated toward the
urushiols in those with
an allergy to them.
Efferent phase
The activated T cells
reach the epidermis
within about 48 hours
and they begin
releasing cytokines,
which recruits more T
cells and causes
dermatitis.
This picture shows severe
dermatitis caused by
poison ivy.
Resolution phase
Ultimately, T cells and macrophages release
cytokines that will stop the response. The
whole process can take up to 3 weeks in
severe cases.
What else is affected?
The same immune reaction occurs when
urushiols are inhaled, with sometimes
severe respiratory reactions.
When urushiols enter through the skin they
also enter the blood stream and have
been found in many other organs, but no
allergic reaction occurs there.
Sources
Information source
McGovern, T.W. Toxicodendron Dermatitis; Identification,
Immunological Mechanisms, Diagnosis, and Treatment.
Professional Educations Services Group
Photo sources
http://www.i-med.ac.at/ahe/histologie-embryologie/arbeitsgruppepfaller-en.html (Photo slide 6)
McGovern, T.W. Toxicodendron Dermatitis; Identification,
Immunological Mechanisms, Diagnosis, and Treatment.
Professional Educations Services Group (All other photos and chart)