ALLERGIES - Medicine for Mountaineering and Other Wilderness Activities - page 326

POISON IVY, POISON OAK, AND POISON SUMAC
Poison ivy, poison oak, and poison sumac ( Fig. 23-1 ) produce an acute contact dermatit-
is—toxicodendron dermatitis—due to the urushiols that are components of their sap. Pois-
on ivy and poison oak are closely related plants found throughout the United States and
Canada and grow as shrubs or vines. Their leaves are shiny and grow in clusters of three,
a distinctive pattern that allows them to be easily recognized. Poison ivy leaves tend to
have smooth edges, and poison oak leaves tend to be more lobulated or serrated, but the
patterns overlap and distinguishing the two is not important. Poison sumac does not have
this identifying feature but grows only in marshy areas east of the Mississippi and is en-
countered much less frequently.
Figure 23-1. Typical appearance of the leaves of poison oak (A), poison ivy (B), and poison sumac (C)
The rash typically develops at the point of contact but may appear at sites that are far
removed.Itusuallyappearsonthehandsandfaceonlyafewdaysaftercontact,butaslong
as a week may pass before it appears at other locations. The rash usually disappears in the
same order it appeared after four to seven days.
Red streaks or patches that itch appear first but are followed in twelve to twenty-four
hours by blisters that typically are arranged in lines. The blisters often break, resulting in
oozing and crusting of the surface. Usually swelling of the underlying tissues, burning,
and itching are present. Scratching should be avoided because it can introduce infection or
cause scarring, but scratching does not spread the rash; the blisters are filled with serum,
not the urushiol that causes the dermatitis.
Treatment depends upon the extent of the rash. If the area covered is small, no therapy
at all may be needed. Calamine lotion may relieve itching. For more extensive eruptions,
itching may be relieved by cool saltwater compresses (2 teaspoons [8 ml or 8 gm] of salt
per quart of water) applied for ten minutes four times a day. A steroid ointment such as 1
percent hydrocortisone canbeapplied inlimited amounts after thecompresses. Individuals