Urushiol-induced contact dermatitis: Encyclopedia - Urushiol-induced contact dermatitis

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.

Urushiol-induced contact dermatitis - Mechanism

Chemically, urushiol is harmless to humans, but when the chemical becomes bonded 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. Since the skin reaction is an allergic one, people may develop an increasingly strong reaction after repeated 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 side-effect, whose existence is mired in controversy, 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, is 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.

Urushiol-induced contact dermatitis - 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® 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.

Urushiol-induced contact dermatitis - 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.

Urushiol-induced contact dermatitis - Treatment

Treatments are designed to treat the effects of urushiol exposure, typically through minimizing the itching (pruritis).

• 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 an additional anti-itch ingredient that is very helpful.
• Corticosteroids. A course of corticosteroids by a dermatologist to neutralize the itch is effective for some people. Commonly prescribed drugs are 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.

Urushiol-induced contact dermatitis - 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.

• 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-polyethoxyethano. 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 a 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.

Urushiol-induced contact dermatitis - 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.

See also

• Poison-ivy
• Urushiol
• Toxicodendron
• Toxin

Category: Dermatology

Adapted from the Wikipedia article "Urushiol-induced contact dermatitis", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki