Poison oakrash is a contact irritational reaction that can transform into blistering spreading rash if the person is sensitized. An oil urushiol is produced by the leaves and acts poisonous if gets on the skin or inhaled as fumes.
What do poisonous plants look like?
Toxicodendron diversilobum (syn. Rhus diversiloba), commonly named Pacific poison oak or western poison oak, is a woody vine or shrub in the sumac family, Anacardiaceae. It is widely distributed in western North America, inhabiting conifer and mixed broadleaf forests, woodlands, grasslands, and chaparral biomes. Peak flowering occurs in May.
Scalloped or lobed leaves, generally appearing in groups of three that resemble true oak leaves is a giveaway of the plant – “leaves of three – let it be!”.
Eastern or Atlantic poison oak (Toxicodendron pubescens or quercifolium) is frequently confused with Eastern poison ivy as it has three grouped leaves that are structurally similar in appearance. A unique feature useful in identification is the presence of clustered small green fuzzy berries on the plant. Distribution is more common in the Southeastern United States but can extend as far north as New Jersey. The leaves of both western and Atlantic poison oak change colors in the fall time and drop off in the Western species.
Symptoms and Signs of allergy
Like other members of the genus Toxicodendron, T. diversilobum causes itching and allergic rashes in many humans after contact by touch or smoke inhalation. Sensitization and reexposure are caused by immune cells T-lymphocytes by a type IV cell-mediated hypersensitivity reaction to urushiol. This is different from typical allergic reaction when histamine from mast cells causes immediate type of reaction.
Here are poison oak local symptoms (appear only on the skin that touched a plant):
Severe itching and redness that is usually appears first and continues until reaction completely stops
Swelling and oozing of the skin tiny blisters
Tiny blisters merging into large bullae and popping with slogging of the upper skin
Crusting and discoloration of the areas
Poison oak can produce severe symptoms in sensitized people or in inhalation of fumes:
Local rash starts spreading everywhere without a pattern
Malaise and headache
Severe itch and pain
Severe oozing of the skin
Cough/wheezing, difficulty breathing
Fever and chills
Signs of a life-threatening allergic reaction
In rare situations people who are hypersensitive to urushiol and present with rapid onset of widespread symptoms within a few hours. Especially problematic is an inhalation of the urushiol fumes. Recently California has huge fires of the hills densely populated with poison oak plants, which produced a lot of poison oak reactions during unhealthy air days.
When to go to the emergency room with poison oak?
If the areas around eyes or on the eyelids develops rash and blisters
If the sensitive area of the groin and sex organs gets involved
If a rash spreads fast all over the body
If you develop difficulty breathing, swallowing
Severe systemic signs – dehydration, dizziness, fever
Eye symptoms with poison oak
It is difficult to determine if the rash is spreading because of the previous sensitization, or because you did not wash off all the oil of the poison oak. Even if you touched something right after the exposure (boots, shoe laces, car wheel or keys) the oil may stay preserved on these surfaces for a long time.
So, if you touched something and then rubbed your eye – you may be in trouble! Just like any oil the poison oak usushiol can get inside the eye and on the eyelids and cause severe contact reaction. Symptoms of the eye poison oak:
Burning and itching of the eye or eyelid
Swelling of the eyelid (sometimes it is not possible to open the eye)
Red eye (redness and swelling of the conjunctiva)
Blisters and rash on the eyelids
Involvement of the eye is an emergency – you need to see a doctor right away!
Conditions confused with poison oak
Several other conditions may be confused with Toxicodendron toxicity, and a careful history and physical examination are necessary to differentiate between them. Herpes zoster often presents as a vesiculopapular rash but follows a dermatomal pattern that doesn’t cross the midline of the body. It is also often preceded by pain in the affected area and would not have a history of environmental exposure. Phytophotodermatitis is another potential mimicker, as it follows a similar timeline.
Differentiating factors include plant exposure on sun-exposed areas of the body and the absence of pruritus. Irritant dermatitis is usually sudden in onset and associated with exposure to metals or other irritating compounds with distinct dermal patterns.
Other arthropod bites such as bed bugs (Cimex lectularius) or scabies (Sarcoptes scabiei) may present similarly and be pruritic but lack the appropriate timing and are typically non-vesicular. Scabies has a characteristic burrowing pattern, while bed bug bites tend to have a rapid onset in skin findings.
How Are Allergies to Poison Plants Diagnosed?
The diagnosis is mainly clinical and based on the history of exposure and ruling out other factors.
Allergy patch testing is widely available and may be useful in identifying patients with severe urushiol sensitivity, or when the diagnosis is difficult.
Skin biopsy may also be needed if the story is not clear or if the rash continues despite all the measures and treatment.
Toxicodendron dermatitis is typically self-limited and resolves within a couple of weeks with just supportive measures.
First and the upmost important step is to eliminate the oil from the skin and decontaminate everything that could have been touched by hands or the plant itself.
Specific instruction should be given to clean under fingernails as they are commonly missed. Mild detergents are a reasonable choice when compared to expensive alternatives. Cool, moist compresses, oatmeal baths, calamine lotion, and topical astringents are used to control severe itch and blisters.
Desensitization seem to work in certain cases, but needs to be continued for all life. Homeopathic oral preparations of poison ivy are used by patient and natural doctors, especially in children and seasonal workers.
Topical and oral antihistamines are another group of commonly taken medications to decrease itching.
Moderate to high dose topical or systemic corticosteroids are given to significantly ill patients or to those who previously has severe reaction. They are beneficial early in the disease course, particularly before the appearance of papules or vesicles. We recommend to keep prednisone at home if you are one of these people, and take it immediately if the first signs of poison oak rash appears (and you know exposure might have happened).
Alternatives for patients who are not candidates for systemic corticosteroids include the application of moderate strength topical corticosteroids with an occlusive dressing for 24 hours that is then repeated 48 hours after initial application. I have to mention that this measure will not work on the face.
The only way to prevent poison oak is not to touch or inhale it. Well, if you already know you have reactivity – try not to, and do this:
Avoid hiking through the bushes in the places where it could grow
Wash your dog if it runs off leash through the bushes
De-weed your backyard
Use paved walks while in parks
Always wash your hands after a nature walk or backyard work
Is a Poison Plant Rash Contagious?
No, poison oak rash is not contagious. If other family members got the rash but did not go hiking with you, that means some other objects in the house or car got contaminated. Try to figure out what can still contain the oil and, if needed, re-wash ALL clothes.