Poison-oak
Atlantic Poison-oak ( Toxicodendron pubescens or Rhus pubescens) is an erect shrub that can grow to 1 m (3 ft) tall. The leaves are alternate, with three leaflets on each. The leaflets are usually hairy, and are variable in size and shape, but most often resembling white oak leaves. The leaves are usually 15 cm (6 in) long, turning yellow or orange in autumn. The fruits are small, round, and yellowish or greenish.
Distribution
This species is native to the South-eastern United States westward to Texas and Oklahoma.
Habitat
Atlantic Poison-oak can be found growing in forests, thickets, and dry, sandy fields.
Caution
All parts of this plant contain Urushiol, which can cause severe dermatitis in some individuals.
Western Poison-oak or Pacific Poison-oak (Toxicodendron diversilobum or Rhus diversiloba) is found only on the Pacific Coast of the United States and of Canada. It is extremely common in that region, where it is the predominant species of the genus; the closely related Atlantic Poison-oak (T. pubescens) occurs on the Atlantic Coast.
Western Poison-oak is extremely variable in growth habit and leaf appearance. It grows as a dense shrub in open sunlight, or as a climbing vine in shaded areas. Like Poison-ivy, it reproduces by creeping rootstocks or by seeds. The leaves are divided into 3 leaflets, 3˝ to 10 centimeters long, with scalloped, toothed, or lobed edges- generally resembling the leaves of a true oak. Western Poison-oak is found only on the Pacific Coast, where it is common, and ranges from Southern Canada to the Baja California peninsula. It is one of California's most prevalent woody shrubs, and is often found in oak woodlands. In comparison to true oaks, the leaves will tend to be rather more glossy.
Toxin
Western Poison-oak leaves and twigs have a surface oil that is an irritant. Depending upon individual
susceptibility (85% of humans will develop allergic reactions) and exposure, the symptoms can range from trivial to life threatening. The common effect is an irritating itchy rash, often accompanied with blistering of the skin. Before the oil is removed, it can be transferred from one part of the body to another, from one person to another by contact or by transfer through an object (such as an automobile seat belt), from a pet to a person, or from clothing to skin when clothes are prepared for washing. If exposed, the recommended immediate treatment is to wash the exposed area with Tecnu (a strong soap that can be picked up at most west coast pharmacies) and cold water. Warm water will tend to open pores on the skin and will lead to deeper irritation.
After the oil has been removed, the poison-oak cannot be spread by contact with an affected area or by scratching. However, scratching can open the skin especially in cases with significant blistering, making it possible for the skin to become infected by
opportunistic bacteria (known as a secondary infection).
Mild cases of poison-oak rash are treated with calamine lotion and other drug store aids while severe cases may require medical treatment and even hospitalization. Inhalation of smoke from burning poison-oak can result in life-threatening lung damage.
For more information on poison-oak rashes, see Urushiol-induced contact
dermatitis below
Quotation
"In spring its ivory flowers perfume the sunny hill or sheltered glade, in summer its fine green leaves contrast refreshingly with dried and tawny grassland, in autumn its colors flame more brilliantly than in any other native: but one great fault, its poisonous juice, nullifies its every other virtue and renders this beautiful shrub the most disparaged of all within our region."
- John Thomas Howell: Marin Flora
Note on name hyphenation
The hyphenated form "Poison-oak" is used, rather than "Poison Oak" to clearly indicate that it is not a variety of oak, just as "Poison-ivy" is not a variety of ivy.
Urushiol-induced contact dermatitis
Urushiol-induced contact dermatitis (also Toxicodendron dermatitis and
Rhus dermatitis) is the medical name given to allergic rashes produced by
urushiol oil contained in various plants. This includes the genus
Toxicodendron (including poison-ivy, poison-oak, and poison sumac), as well
as other plants in the family Anacardiaceae (mango, Rengas tree, Burmese lacquer
tree, India marking nut tree, and the shell of the cashew nut), and even
unrelated plants such as Ginkgo biloba.
The American Academy of Dermatology estimates that there are up to 50 million
cases of urushiol-induced dermatitis annually in the United States alone. It
accounts for 10% of all lost-time injuries in the United States Forest Service.
Poison-oak is a significant problem in the rural western and southern U.S.,
while poison-ivy is most rampant in the eastern U.S. Dermatitis from poison
sumac is not common, but it heavily impacted construction work on Disney World
in Florida.
Mechanism
Chemically, urushiol is harmless to humans, but when the chemical bonds to
skin cells it initiates a T-cell mediated immune response. This immune response
is directed towards the complex of urushiol derivatives which are bound up in
the skin proteins. The result is an allergic eczematous contact dermatitis
characterized by redness, swelling, papules, vesicles, bullae, and streaking.
People vary greatly in their sensitivity to urushiol. It is thought that about
20 to 40% of individuals are not significantly affected by it, although at least
25% of the CPE have strong reactions to "poison ivy". Since the skin reaction is
an allergic one, people may develop an increasingly strong reaction after
repeated exposures, or show no immune response on their first exposure, but show
definite sensitivity on following exposures.
Normally, it takes about twenty-four hours for the rash to first appear,
though it may worsen during the next few days and may appear to spread, when in
fact what is happening is that areas that received a lesser dose are latently
reacting. The rash takes one to two weeks to run its course, but normally does
not leave scars. Severe cases will have small (1-2 mm) clear fluid-filled
blisters on the skin. Pus-filled vesicles, containing a whitish fluid, may
indicate a secondary infection. Most poison-ivy rashes, without infections, will
self-resolve within 14 days without treatment.
One disputed theory holds that a systemic reaction is possible if urushiol
gets into the bloodstream (via an open cut, popping of blisters, etc.) This
manifests itself as new rashes seen days later on unusual parts of the body.
Critics of the theory suggest that such "spreading" is an illusory effect as
urushiol spreads on hands and clothing after initial contact, and some areas of
skin simply have a delayed reaction. New outbreaks may also be the result of
contaminated bedding, dirty clothes, and pet contact.
The causative agent, urushiol, does not spread once it has bound with a cell
membrane, and it is not found in weeping blisters. Thus, once the oil and resin
has been thoroughly washed from the skin, the rash is usually not contagious.
Excessive scratching may result in secondary infection, commonly by
staphylococcal and streptococcal species. These may require the use of
antibiotics.
Prevention
Common-sense measures to avoid skin irritation include avoiding contact with
the plants, staying out of dense brush, wearing long clothes, and changing
clothes after coming in contact with the plants. Dogs may return from
unsupervised romps covered with the urushiol, and then transmit it to humans
either directly or through carpets and furniture. However, poison-ivy and other
Toxicodendron related plants should never be burned. DO NOT BURN poison ivy
plants! Burning brush that includes Toxicodendron can be fatal, since the
smoke can cause damage to the lungs, resulting in pulmonary edema.
Preventing exposure to poison-ivy, poison-oak or poison sumac involves ways
of preventing the oil from getting on the skin.
- Wear long clothing.
- Avoid plants that even look like poison-ivy, poison-oak or poison
sumac.
- Clothing that has been exposed to Toxicodendron should be washed in hot
water before use, including shoe and boot laces.
- If you must wear short clothing, put thick lotion on areas that may be
exposed to Toxicodendron, like the legs. A suntan oil may work even better.
- Before handling tools that have touched Toxicodendron, wear gloves, then
wipe the tools with alcohol immediately after using them, or throw them away.
Garden implements may be washed with detergent and hot, running water.
Toxicodendron species are very resistant to many herbicides. Some herbicides
will not destroy the roots, allowing the plant to grow back the following year.
Glyphosate-based Roundup® (especially when mixed with Remedy, from Dow
AgroSciences, which is oil soluble); and Rodeo® from Monsanto will eventually
kill Toxicodendron, but may require repeated applications, depending on the
solution concentration used. Some people recommend using a triethylamine
salt-based brush killer such as Ortho Brush-B-Gone®, while other recommend
spraying or applying gasoline or kerosene on the plants, using appropriate
safety precautions.
Another option is to physically pull up all the vines and roots, but one
should wear gloves and long sleeved clothing, then wrap the plants in a strong
plastic bag and bury them or dispose of them in a landfill. Wash with soap and
water immediately after any possible contact, and take special precautions to
prevent children from having any secondary exposure to objects that have been in
contact with the plants after they have been removed.
First aid
Immediately wash exposed skin thoroughly with soap and water. Folk
wisdom includes contradictory advice about whether to wash with cold or hot
water after coming in contact with the oil. Care should be taken to avoid
spreading the oil over an even wider area. All exposed equipment and clothing
should be washed with detergent, and exposed pets should be bathed to prevent
recontamination.
Soap is important. Urushiol is a hydrophobic oil, and is not washed off by
plain water. In lieu of soap, people have had success in lessening the rash by
wiping the area clean with alcohol in order to break down the oil. Laundry
detergent or Fels-Naphtha soap are more effective, though vigorous rubbing is
necessary. Note that the application of any such chemicals to the skin might
produce its own adverse reaction. For similar reasons, one should not use
gasoline or Lysol, although old wives' tales mention using these as remedies.
Removal and washing of clothing which may have been exposed is recommended to
prevent further exposure. If in the woods, clay from a clean creek bed and
plenty of water may be used as a substitute for soap and water to rinse affected
arms and hands to remove poison-ivy toxins before a reaction occurs.
There are several pharmaceutical measures that may be taken to prevent or
lessen a rash. Zanfel and Tecnu are commercial preparations designed to 'unlock'
urushiol from the skin. If applied within 20 minutes of exposure to poison-ivy,
these may be effective in completely preventing an outbreak. Zanfel, the more
expensive of the two by far, may be effective at any stage of a poison-ivy
outbreak. Once an outbreak has occurred, cold compresses, calamine lotion,
antihistamines, and hydrocortisone ointment are commonly used to abate the
symptoms.
If the rash is severe or if it does not resolve within 14 days, or if the
rash affects the face, eyes, mouth, or genitals, a doctor should be consulted.
While recovering from poison-ivy, special efforts should be made to change
bed sheets, pillow cases, and clothing that contacts the affected areas
regularly.
Treatment
Treatments are designed to treat the effects of urushiol exposure, typically
through minimizing the itching (pruritus).
- Cold air. A fan or air conditioner blowing on the rash can be very
effective at minimizing the itch.
- Warm water. Hot showers are effective for some in temporarily
relieving the itching. For others, they make the itching worse, presumably
because warm water may trigger a histamine response.
- Hot water/air. Some people find effective itch relief in deliberately
triggering a histamine response, to the point of locally depleting the histamine
in the skin. Hot water, or, more practically, hot air from a blow dryer applied
just until it hurts, will release most of the histamine in the skin. It takes
approximately 8 itch-free hours for the skin to replace the histamine.
- Calamine lotion. Calamine lotion is the most commonly used lotion to
help dry affected areas. The brand name "Caladryl" product (easily confused with
simple calamine) contains camphor as an additional anti-itch ingredient to
increase effectiveness.
- Corticosteroids. A course of corticosteroids by a dermatologist to
neutralize the itch is effective for some people. Commonly prescribed drugs
include prednisone and betamethasone (Diprolene). The downside is that these are
prescription drugs and incur an extra expense.
- Antihistamines. The family of antihistamine drugs suppresses the itch
by affecting the body's histamine response. Commonly prescribed drugs are
diphenhydramine (Benadryl) and loratadine (Claritin).
- Cala-Gel. This is a clear gel manufactured specifically for
Toxicodendron dermatitis. It is available over-the-counter in the United States.
- Natural remedies. Other home remedies, mostly ineffective, include
acorn tea, banana peels (rub the inside of the peel on the affected area), birch
tea, bulrush, burdock, cattail, chicory, comfrey, hemlock, milkweed, mint,
spicebush, sumac (non-poison), sweet fern, thistle tea, and yucca. One
traditional remedy is to find plants of jewelweed (Impatiens species),
and to take the whole plant, crush it into a ball, and vigorously rub it into
the exposed area. Or, crush some jewelweed stems in a container, and use a
cotton ball to soak up the juice. Spread it on the rash as soon as possible.
Poison-ivy is often found growing in the vicinity of Jewelweed, though the
converse is not true. The efficacy of this remedy is however disputed, with some
tests showing no benefit from Jewelweed. Rubbing alcohol may also be used to
help dry the rash and prevent infection.
- Homeopathic remedies Ingestion of young leaves in the spring, milk
from goats that feed on poison ivy, and commercially available extracts are used
to desensitize the immune system to urishiol.
Cure
No vaccine has been developed to counter urushiol symptoms, so "cures" are
generally held to be those products that physically remove the urushiol. After
about 15 minutes of exposure, the urushiol is chemically bonded to the skin and
can only be removed with pharmaceutical products, some of which will not work as
effectively for some people as it will for others.
- Tecnu. Originally developed as a treatment for radiation exposure, it
was discovered later that Tecnu provided some relief for poison-ivy exposure. It
is a milky liquid and the main active ingredient is
octylphenoxy-polyethoxyethanol. The four octyl groups of this chemical are too
large to surround the non-polar molecules in the urushiol, which remains
partially active and requires multiple applications. Also, the chemical makeup
of the product requires that it be applied no later than eight hours after
exposure to urushiol. In the United States it is sold over-the-counter in larger
drug stores for between $2 to $16, depending on quantity.
- Zanfel. Developed in 1999, this paste uses an ethoxylate molecule
with the large octyl groups removed. This allows the molecule to "wrap" around
the non-polar molecules of the urushiol and inactivate it. The other ingredient,
sodium lauryl sarcosinate, allows the ethoxylate to form a micelle around the
urushiol molecule. This creates a large molecule that contains flexible
non-polar groups and soluble polar groups, allowing it to be rinsed away with
water. The item is sold over-the-counter in the United States for between $30
and $40 an ounce.
Common Myths
There are many myths that deal with Toxicodendrons such as poison-ivy. Most
have been discredited widely, but there are still some that remain.
- The fluid from the resulting blisters spreads poison-ivy to others.
- Poison-ivy is harmless when the leaves have fallen off.
- Ice, water, soap, lotions, dry cold air, can help cure poison-ivy rash
faster. In reality, skin cells react to the urushiol even after the urushiol has
been washed off, and the methods listed are for soothing the rash.
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