Poison ivy update

Poison ivy update

By William L. Epstein, MD, Jere D. Guin, MD, and Howard I. Maibach, MD

Many children will have an allergic reaction to poison ivy, poison oak, and poison sumac during the coming season—and many of the afflicted will be miserable. What can you do to help patients prevent the problem and to ease their discomfort when they do fall prey?

Many children who fill your waiting room in late spring and summer will appear with blistering, itchy rashes—the result of an encounter with poison ivy, poison oak, or poison sumac. In addition to relieving the discomfort, you can help patients and their parents learn how to recognize the plants and protect themselves so they can enjoy the outdoors without paying for the consequences.

Poison ivy, oak, and sumac are all members of the family Anacardiaceae, genus Toxicodendron. These related plants look different, although they share some general features (see Table 1).¹ What's surprising is that the poison ivy growing in your area may not look anything like the poison ivy found halfway across the country. And poison oak indigenous to the East Coast is very different from poison oak out West. However, the dermatitis these plants cause—and the approach to treatment—is similar. Therefore, unless a specific plant is intended, this article uses the shorthand "poison ivy" to refer to poison ivy, oak, and sumac.

Getting "stung" by poison ivy

Although not all the children exposed to these plants will break out in a rash, many have the capacity to develop a sensitivity. The discrepancy lies in the opportunity for exposure and concentration of the allergen. Children who are immunodeficient, such as those with leukemia or AIDS, may actually be less susceptible because allergic contact dermatitis is a cell-mediated immune reaction.

The prevalence of poison ivy dermatitis also seems to be reduced in those who have asthma, hay fever, and other types of allergies. This may be because they have diminished immune function or because they are less likely to engage in outdoor activities that expose them to the plants.

The "poison" in these plants is the chemical urushiol, which is found in the sap. All parts of the plant—leaves, stems, roots, flowers, and berries—contain urushiol. An intact plant is not capable of triggering an allergic reaction. Pulling weeds or cutting the plant when mowing can release toxic material. A gust of wind may be enough to crack a leaf and allow the sap to leak. The brush of a hiker's leg, a child's lost ball, or a gardener's tool can break a stem and allow urushiol to seep out.

When exposed to air, the yellowish- to-clear urushiol will turn black. Black spots on a plant are a good indication that it is poison ivy or one of its cousins. These are seen where there is trail damage or where insects damage a leaf. Sensitive persons should avoid touching any plant with black spots, whether or not it looks like the poison ivy, oak, or sumac common in your area.

A quick fix after exposure?

Urushiol is a haptene and rapidly penetrates the skin to combine with skin proteins. A person who is aware of making contact with poison ivy may be able to prevent an eruption by taking quick action soon after contact. The impact of urushiol can be lessened by washing with plain water. Adding soap or using an organic solvent or oxidizing agent, such as hydrogen peroxide, is even better.

Many rashes are the result not of direct contact with a plant but of transfer of urushiol from the hand to another part of the body. For example, someone who has touched poison ivy wipes a sweaty brow, and later the forehead is bumpy and itchy. Urushiol trapped under the fingernails will land on skin idly scratched, so it is important to scrub under the nails after touching poison ivy. The rash itself is not contagious—that's one of many persistent myths about poison ivy (see "Separating fiction from fact").

Because urushiol is an oil, it penetrates the skin easily. Whatever has come into contact with poison ivy should be washed well—clothing, tools, sports equipment, even pets. Animals can carry the oil on their fur and leave it on furniture or on the skin of an affectionate human companion. An unsuspecting athlete might end up with dermatitis after retrieving a ball that rolled into a poison ivy patch weeks earlier. Someone who gathers clothes for the laundry could break out after picking up urushiol-soaked attire.

The clinical presentation

The allergic reaction may begin as early as six hours after exposure, with a linear group of itchy, red spots at the point of contact with urushiol. More typically, the onset of symptoms is 24 to 72 hours after exposure. Pruritus and erythema are accompanied by edema, and urticarial plaques and bullae may develop (Figure 1). Linear vesicles or papulovesicles strongly suggest that a rash is caused by poison ivy.

Several days or even as long as two weeks after the initial eruption, the rash may appear on other areas of the body. This has led to the mistaken notion that poison ivy dermatitis is spread by the blister fluid. Actually, there are two reasons why the outbreak may occur in stages. First, the skin that erupts at a later time may have been exposed to less urushiol. The more likely explanation, however, is believed to be a difference in the rate of absorption and differences in skin reactivity at various anatomic sites. The thin skin around the eyes will absorb urushiol much faster than the thicker skin on the arms. Although the hands probably make contact with these noxious plants more often than any other part of the body, rashes are uncommon on the hands because the skin is much thicker.

While not likely to break out itself, the hand often is the transfer agent for urushiol. Many times, a rash that develops on the face or arm may resemble a handprint, and linear lesions may trace the marks of scratching fingers.

Severe edema on the delicate skin of the face and genitalia may be the only symptom of an encounter with a poisonous plant. The genital and perianal areas usually become affected when someone defecates in the woods and either accidentally brushes against poison ivy or selects a urushiol-tainted leaf as toilet paper. In addition, poison ivy dermatitis has been acquired in intimate moments of skin contact by people whose sexual partners failed to wash off urushiol.

Before gathering around the fireplace or campfire, people should inspect the logs for clinging vines, brown rootlets, and black spots of urushiol. Smoke from burning plants that carries particles of the sap can cause a diffuse dermatitis. If inhaled, urushiol may cause bronchitis or pneumonitis. Nearly one third of forestry workers and firefighters in the Pacific Northwest develop rashes or lung irritations from contact with poison oak.² Fatal adult respiratory distress syndrome was recently reported in a man exposed to the smoke of a burning poison ivy plant.³

The diagnosis of poison ivy dermatitis is usually obvious, and the source generally can be determined even in atypical presentations. However, you may have to put on your Sherlock Holmes cap to get to the source of the problem if a patient keeps returning with dermatitis or if the lesions fail to heal in a few weeks. Recurrent or persistent dermatitis indicates repeated contamination with urushiol. The patient may be coming in contact with fomites such as pets, clothing, or tools. Washing every possible source of contamination should eliminate the problem.

Treatment: Rx for suffering

The contact dermatitis from poison ivy is a self-limiting condition. Without any treatment, a mild case will often resolve in about two weeks. But the discomfort is too much for most of the afflicted to ignore. The treatments discussed here do not cure the condition; they simply ease the suffering.

Patients will find relief by using cool compresses with astringents like aluminum acetate solution or soaks with colloidal oatmeal. Calamine lotion is soothing, but products that contain a topical antihistamine, such as diphenhydramine, should be used only with the understanding that sensitization can occur. (Fortunately, sensitization is uncommon.) For children with mild reactions to poison ivy, simple compresses, soaks, and lotions will probably be adequate, and the lesions will then heal spontaneously.

Many experts feel that oral corticosteroid therapy is not the best way to approach the routine treatment of a limited condition like poison ivy. Corticosteroids should be reserved for more serious cases, especially those in which the rash is severe and accompanied by swelling. For some patients, the discomfort may be so distressing that a short course of corticosteroids would be beneficial. In any case, oral systemic corticosteroids can be quickly tapered and discontinued; dosages should be kept relatively small and tailored to the individual patient. For children, the dose of oral corticosteroids should be 1 to 2 mg/kg/day for five to seven days; sometimes a longer course is needed. Injected corticosteroids are warranted in the unusual cases in which urushiol has been inhaled or swallowed. An injection of fast-acting corticosteroids will quickly stop the reaction. Patients in extreme discomfort also may experience quicker relief from injection of medications such as betamethasone sodium phosphate. The earlier the injection is given, the better the relief from symptoms.

Topical corticosteroids such as clobetasol propionate have some usefulness; they may be helpful in treating acute lesions that are not blistering. The full-blown reaction may be avoided if the earliest itchy, red lesions are treated with a potent topical corticosteroid such as mometasone furoate (Elocon Cream 0.1%, with package labeling for children age 2 and older) or fluocinolone acetonide topical oil (Derma- Smoothe/FS 0.01%, with package labeling for children age 6 and older). However, patients rarely come for treatment so quickly. By the time you see most of those afflicted, they already have blisters, and at this point topical corticosteroids will do little good. The corticosteroids in OTC preparations are too weak to be effective.

In rare cases when systemic corticosteroid therapy is contraindicated and the dermatitis is confined to a limited area, topical treatment may be an option. A midpotency corticosteroid can be used with an occlusive dressing applied for 24 hours. The treatment is repeated the next day. The occlusive dressing increases the efficacy of the drug. The principal reason to use antihistamines to treat a poison ivy reaction is that the patient is too miserable to sleep as a result of intense itching. In that case, the sedating effect of antihistamines may be desired. Nonsedating antihistamines probably have no role in the treatment of poison ivy dermatitis.

What role for "natural" remedies?

Over the centuries, many herbal treatments and folk remedies have been touted for poison ivy. Such natural therapies are bound to appeal to some parents who are outdoor enthusiasts. Among the purported herbal treatments for poison ivy are plantain, feverfew, and jewelweed. Despite anecdotal reports that these plants ease discomfort, there is no scientific evidence using humans subjects to support the use of any herbal remedies. However, they may have a soothing effect similar to that of the compresses that have long been recommended by physicians for patients suffering from an itchy rash.

Prevention

Poison ivy is one condition for which the best treatment is prevention. Everyone should learn to recognize the varieties of poison ivy, poison oak, and poison sumac that grow in the areas where they live or play. This is not as easy as it sounds. The plants take many forms, and no single textbook, no matter how thorough, will picture every possible culprit.

Quaternium-18 bentonite is available to prevent poison ivy dermatitis. Marketed as Ivy Block and sold OTC, this lotion forms a claylike barrier against the plant's sap. The active ingredient is an organoclay that has been used for years in cosmetics and has a good safety record.

A multicenter trial demonstrated that quaternium-18 bentonite lotion prevented or diminished poison ivy and poison oak dermatitis in susceptible volunteers.⁴ When applied at least 15 minutes before exposure to the plants, the product provides protection for people who are mildly to moderately sensitive to poison ivy. Stoko Gard Outdoor Cream, another product that forms a barrier on the skin and may help to prevent poison ivy dermatitis, is available from industrial suppliers.

Although people who know they are about to enter an area thick with poison ivy might arm themselves with a barrier lotion, most contacts with the plants are not anticipated. Therefore, other precautions become necessary. Use the accompanying guide to teach the parents and patients to recognize the plants and to take measures to lessen the chance of their suffering a week or two of agony (see "Stay away from poison ivy!" below).

When a known allergen cannot be avoided, a program of desensitization has often been recommended. At one time, preparations for hyposensitization to poison ivy were available. The pruritus and urticaria they caused outweighed their effectiveness, however, and the FDA withdrew approval to market these products. These methods of desensitization depended on administering increasing doses of partially purified urushiol. New approaches based on the concepts of cellular immunity are being explored, although no such desensitization products will be available for some time.

References

1. Guin JD: Plant, in Guin JD (ed): Practical Contact Dermatitis: A Handbook for the Practitioner. New York, McGraw Hill, Health Professional Division, 1995, p 497

2. Stehlin IB: Outsmarting poison ivy and its cousins. FDA Consumer 1996;(Sept):25

3. Kollef MH: Adult respiratory distress syndrome after smoke inhalation from burning poison ivy. JAMA 1995;274:358

4. Marks JG Jr, Fowler JF Jr, Sherertz EF, et al: Prevention of poison ivy and poison oak allergic contact dermatitis by quaternium-18 bentonite. J Am Acad Dermatol 1995;33:212

Suggested Reading

Avalos J, Maibach H: Plant Dermatology. Boca Raton, FL, CRC Press, 1999

DR. EPSTEIN is Professor of Dermatology, University of California, San Francisco, School of Medicine.

DR. GUIN is Professor of Dermatology, University of Arkansas for Medical Sciences, Little Rock.

DR. MAIBACH is Professor of Dermatology, University of California, San Francisco, School of Medicine.

The parent guide on poison ivy may be photocopied and distributed to families in your practice without permission of the publisher.

GUIDE FOR PARENTS

Stay away from poison ivy!

If you or your child has ever had a run-in with poison ivy, poison oak, or poison sumac, you know the results: an itchy, blistering rash. The best way to prevent it is to avoid the plants.

Know the enemy

Poison ivy can be found in most parts of the country. Poison oak grows in the eastern states and along the West Coast. Poison sumac is found mainly in swampy areas in the Southeast. Although these plants look different, the damage they do is similar.

An old saying to help people avoid these plants is "Leaves of three, let them be." That's good advice, but it doesn't go far enough. The leaves may be five for poison ivy and oak; seven to 13 for poison sumac.

Poison ivy comes in many varieties. It's common in wooded areas and also is found near lakes and streams. Poison ivy often grows as a vine, but it can also be a shrub. The leaves are often the first to turn color—red—in the fall. In the spring, the plant has yellow or green flowers or white berries.

Poison oak takes two forms. In the East and South it grows as a low shrub; along the Pacific Coast it may be a tall shrub or a high-climbing vine. The notched leaves resemble those of the common white oak tree. The yellow berries grow in clusters and are all green in summer and off-white in winter.

Poison sumac favors boggy areas. The tall shrub has seven to 13 smooth-edged leaflets on each stem. The berries are green in summer, pale yellow-white when mature.

The best advice is to learn what the problem plants in your area look like. Also, avoid any plant with black spots. Those are marks of urushiol, the substance in the sap that causes the rash.

All parts of these plants contain the sap—not just the leaves but also the vines, stems, roots, flowers, and berries. Do not touch any part of the plant. The sap can last throughout the winter, so choose your firewood carefully!

How to protect yourself

Whenever your family is planning to be in an area where poison ivy, oak, or sumac grows, have everyone take these protective steps:

• Wear long sleeves and long pants, even in hot weather.

• After contact with poison ivy or its cousins, react fast. The sap will come off with water, but it is best to wash it off shortly after contact. Scrub under the fingernails, too, to get rid of any sap there.

• Be careful not to rub the sap into broken skin or spread it to other areas of the body. For example, warn children not to rub their eyes with a hand that may have touched a poisonous plant.

• Avoid hugging a pet who's been romping in poison ivy until it has had a bath. Animals can carry the sap on their fur.

• Launder clothes that may have come into contact with poison ivy. Be careful not to touch any sap that is still on the clothes.

• To handle plants, wear vinyl gloves. Urushiol can soak through cloth and even rubber, but vinyl is resistant.

• After working in the garden, rinse off tools.

What to do if you break out

If the itch is bad, the doctor will recommend medication. Follow your doctor's instructions.

Most people find cool, moist compresses helpful. Oatmeal soaks (Aveeno) also bring relief. A lotion like calamine is soothing, but don't use products like Benadryl, which contains a drug that can make the rash worse.

Try to prevent scratching, which can break the skin and lead to infection. The rash isn't spread by scratching, however, unless there is sap under the nails.

Don't worry about spreading the rash to others. It is not contagious. The only way to get a reaction to poison ivy is to come into direct contact with the sap.

If you don't know the source of the rash, do some investigating. Search the yard and other areas for plants. Until you find them, you risk more outbreaks. Other possible sources are:

• Pets

• Yard tools

• Sports equipment

• Clothing worn while playing outdoors, hiking, or gardening

• Topsoil

• Firewood

Jere Guin,Howard Maibach,William Epstein. Poison ivy update.

Contemporary Pediatrics

2000;4:54.