Hollywood has a lot to answer for. Those who hear the words “poison ivy” and immediately think of Uma Thurman cavorting sensuously in 1997’s Batman and Robin movie may find themselves dangerously distracted. A potential consequence of this, on the trail, is a brush against a plant known as the “itchy rash vine” (1).

The nickname may not be hugely imaginative but it is accurate. The plant is indeed poisonous and a brush against its leaves can leave you with an angry red rash that can be extremely uncomfortable.

It isn’t the only North American plant that’s out to get you either. Two close relatives of poison ivy, poison oak and poison sumac, can be equally unfriendly. If, a few days after a wilderness adventure, you find yourself with a red rash characterised by bumps, blisters, swelling and itchiness (2), the chances are your skin has been in contact with urushiol, an oil contained within all three plants that produces an allergic reaction in most humans.

Fortunately, there are steps you can take to keep urushiol at arm’s length. The Center for Disease Control and Prevention (CDC) recommend that those moving through areas with poisonous plants should wear long sleeves, long pants, boots, and gloves and that any clothes that come into contact with the plants should be washed separately at a high temperature (since “urushiol can remain active on the surface of objects for up to 5 years”).

Of course, in order to know if you’ve been in contact you’ll need to become something of an amatuer horticulturalist. Read on to find out how to pick out poisonous plants and how to react if the worst comes to the worst and you do come into contact with them. It could save you some serious discomfort…      

Where they grow and how to avoid them?

Poison Ivy

Poison ivy, or toxicodendron radicans as it is not better known, is a plant that, according to botanists, should be “admired for its versatility” (3). The plant can grow along the ground to a height of around two feet, blossom to become a four-foot high shrub in its own right or kiddyback onto trees as vines that can climb as high as 100 feet (4).

The plant is common, found in a number of natural and human-influenced environments throughout Mexico, the United States and Canada, and has a propensity to “grow on the sides of trails” (5), highlighting the danger it poses to trekkers.

This map illustrates the distribution of poison ivy throughout the United States and highlights that it is primarily found in the Eastern states, where it is a native plant.

However, the versatility has already been highlighted and, according to several sources (6, 7), a variant of the plant known as Western Poison Ivy is present in most Western states with the exception of Southwest states such as California. Western Poison Ivy distribution is plotted in this map.

The key difference between Eastern and Western is that Western, the non-native variety, is “only a ground vine” (8). It also isn’t as prevalent as Eastern but is every bit as inflammatory to humans if touched.

What Does Poison Ivy Look Like?

Leaves

Ever heard the phrase “leaves of three, let it be”? It’s a starting point in the identification of poison ivy. It always produces leaves in bunches of three, with the middle leaf slightly longer than the two to either side (9).

There are, of course, plenty of harmless plants with three leaf clusters. One of the reasons it’s tough to spot is that, aside from the plant’s three leaf pattern “there is very little about its leaf shape that is consistent” (10) – some poison ivy plant leaves have smooth edges, others have ragged edges, etc.

If you are an inexpert identifier of plants who wishes to avoid rashes then, really, your safest bet is to avoid all three-leafed plants like the plague!   

The Seasons

The appearance changes with the seasons (11).

In summer the plant is green – not particularly helpful as an identifier since the vast majority of plants are green at this time of year! However, in summer some produce small orange and light green blossoms that can give it away (12)

In the spring and fall it can be easier to spot. Budding/aging poison ivy leaves show in shades of orange and red that are most striking, often spectacular, in the fall. At these times of year you’ll definitely want to avoid orange/red three-leafed plants!    

In winter it loses its leaves. Critically, however, it doesn’t lose its urushiol oil, meaning those who brush against it still risk developing a poison ivy rash. The Spruce suggest two ways of picking out poison ivy in the winter:

1. Look out for any berries left on the tree. The berries (which develop from the small summer flowers) are pale or white in appearance.
2. Identify the plant by its aerial roots. These roots appear as “hairy vines.” It doesn’t seem likely that you’d want to touch a plant with “hairy vines,” but you’re advised to resist the impulse should you have it!

Poison Oak

Poison Oak has much in common. Indeed, one variety of poison oak, Atlantic Poison Oak, has so much in common with poison ivy “many people use the two terms interchangeably.” (13)

The most notable difference is that poison oak leaves tend to have rounded rather than pointy ends and have a “wavy appearance (also described as scalloped), similar to oak tree leaves” (14). It is this resemblance to oak tree leaves that gives poison oak its name. Obviously.

This poison oak map shows the distribution of the two varieties of poison oak in the US. As the names suggest, Pacific Poison Oak grows along the west coast and Atlantic Poison Oak along the east. Pacific Poison Oak is by far the most numerous of the two and the biggest problem since although it grows “almost entirely in California, a lot people live there.” (15)

A lot of people hike there, too!

What Does Poison Oak Look Like?

Leaves

The vast majority of poison oak plants grow in clusters of three. However, it should be noted that, “some varieties display five or seven per cluster.” (16)

In these cases the rounded, wave like appearance of the leaves can be key to identifying poison oak. The presence of yellow/greenish flowers and/or pale/white berries, further similarities, can also help zero in on poison oak (17).

The Seasons

Seasonal colour changes are one of the key ways in which poison oak differs from poison ivy. In spring the leaves tend to be a glossy green, in summer they turn yellow-green or pink and in the fall they tend to be yellow then dark brown before dropping off for winter.

Look out for poison oak growing as a “as a small shrub in open spaces or as a climbing vine in shaded forest areas.” (18)

Poison Sumac

“Leaves of three, let it be” will not protect you from poison sumac! Poison sumac stems contain between 7 and 13 leaves arranged in pairs (19) with a lone leaf at the end of the stalk.

Another clear difference between poison sumac and its urushiol rich contemporaries, is that it grows as a tree or as a standalone shrub between five to 20 feet tall (20).

These trees are exclusively found in extremely wet areas – think swamps or wetland – and, as this map shows, only in the Eastern states. Somewhat confusingly, poison sumac is not related, taxonomically, to other sumac trees.

It is perhaps best to think of poison sumac as the wetland relation of poison ivy and poison oak. Sumac wears a cunning disguise to try and hide its resemblance to better known poisoners but don’t be fooled!

What Does Poison Sumac Look Like?

Leaves

As mentioned above, poison sumac contains 7-13 leaves arranged in pairs with a lone leaf at the end of each stem. The leaves have quite a distinctive form. They are oval, have smooth edges and tend to be between two and four inches in length (21) – though you’ll want to avoid measuring them unless you have sturdy gloves on!

The Seasons

Poison sumac leaves are bright orange in spring, green in summer and a darkish red in the fall, before dropping off.

Poison sumac remains poisonous in winter, even when bare of leaves. Look out for small green and yellow berries that grow in clusters, like grapes, to help identify poison sumac trees in winter. Even if the berries have dropped off the stems should resemble grape vines – a sign that they should be avoided. (22)

Do not be tempted to try and make wine from those grape-like berries – it’ll be the worst hangover you’ve ever had!

Removing Poison Ivy, Poison Oak and Poison Sumac from Your Property

Now that you’re aware of the dangers these plants and how to identify them you may feel an urgent desire to remove them from your garden. The Mother Nature Network detail two ways to get rid of poison ivy:

Suit up and rip it right out of the ground!

• Please take note of the “suit up” part of this instruction. Since you’ll be in close contact with the plant you’ll want to cover every part of your body that could be in contact with it. Robust gloves are a necessity and you may even want to duct tape them to your shirt (and your socks to your pants) to create an impenetrable suit of cotton armour!
• Set about ripping out the plant, ensuring that you dig at least eight inches beneath it to eliminate all roots and lay cardboard on the area to guard against regrowth.
• Dispose of the plant carefully. It should never be burnt as it is toxic to inhale and the smoke can spread the plant to other areas. Instead, seal it up in a garbage bag and leave it out for refuse collection.
• Afterwards, wash all your clothes at twice the recommended temperature to cleanse them of the plant

Spray it to death!  

• Measure out a gallon of water and mix in a cup of salt and a tablespoon of dish soap.
• Add the mixture to a sprayer and spray only on the ivy (the mixture will kill any other plants it hits, too)   
• This is best done on a day when no rain is forecast, since rain can dilute/wash off the mixture, and may need to be repeated a few times until the plant is killed

Poison oak can also be eradicated by the above two methods, but The Spruce suggest that cutting the plant down to stumps then treating it with a herbicide, the same method recommended for the removal of poison sumac, is a better way to proceed.

To treat poison oak and/or poison sumac in this way:

• Wait until the growing season when the plant will be most vulnerable to attack!
• Wear similar protective clothing to that detailed above for ivy and wash at a high temperature after use. Note that rubber and latex gloves do not provide sufficient protection from urushiol (23). Thicker gloves will be required.
• Prune the tree/shrub down to a height of between a few inches and one foot off the ground and apply the herbicide straight away. Do so on a still, rainless day to avoid herbicide being blown over other plants and/or washed off by rain.
• Cut branches and leaves should be disposed off (not burnt!) in the same manner as ivy leaves

Causes and Symptoms

As they all contain the same inflammatory oil, urushiol, contact with each of the shrubs will induce a similarly nasty, itchy red rash on the skin of most people who come into contact with it. As is the case with any allergic reaction there are degrees of vulnerability. A lucky 15% are all but immune to urushiol (24). The remaining 85% of us are likely to incur an unpleasant allergic reaction…

How do you get this reaction?

According to the CDC the cause is usually simple – direct skin-to-plant contact with a the plant.

That being said, as urushiol can remain active on the surface of objects for up to five years it is also possible to obtain a rash by touching clothes, tools or other objects that have previously been in contact with the poisonous shrubs. To avoid this scrub any items with warm water and soap after use to remove urushiol.

Finally, exposure to the smoke of burning the plants can cause airborne urushiol to land on your skin or, even worse, attach itself to your eyes, throat or nose!

What are the symptoms?

The American Academy of Dermatology (AAD) list the symptoms of urushiol exposure as:

• Itchy skin.
• Redness or red streaks.
• Hives.
• Swelling.
• An outbreak of small or large blisters, often forming streaks or lines.
• Crusting skin (after blisters burst).

The rash can appear any time between a few hours and a few days after exposure and is typically extremely itchy. The symptoms will, however, usually heal within a week or two, providing they aren’t worsened by severe scratching or a spreading of the rash to other parts of the body (which can occur when scratching of the area transfers urushiol oil to the hands then other areas of the body). (24)

It should be noted that, angry and inflamed as these rashes may look, they are not contagious. “You cannot give the rash to someone else,” the ADD note. “Even if the person touches the rash or the fluids in the blisters, the person cannot get the rash. The person has to touch the oil to get the rash.”

How Does the Rash Affect You?

Check out this link for a collection of stories from people who suffered from severe urushiol reactions as a result of doing inadvisable things like hacking weeds wearing shorts and eating marshmallows roasted on poison ivy stalks. Ouch!

For most people symptoms will be unpleasant but not serious. The ugly appearance of the rash and itchiness are likely to be the primary concerns.

Nonetheless, the Mayo Clinic note that there are cases when urushiol reactions can be more serious and require treatment. They note that you should see your doctor if:

• Your reaction is severe or widespread
• You inhaled the smoke from burning the plant and are having difficulty breathing
• Your skin continues to swell
• The rash affects your eyes, mouth or genitals
• Blisters are oozing pus
• You develop a fever greater than 100 F (37.8 C)
• The rash doesn’t get better within a few weeks

Treatments

If you come into contact with urushiol oil timing is everything. To be precise, you “have about 10 minutes before the sap penetrates the lower layers of your skin and binds to its cells, at which point an allergic reaction will set in” (25).

During this period rinsing the skin, scrubbing it with a mild detergent soap (not a fatty soap as it can spread urushiol oil rather than remove it) and applying rubbing alcohol to the area can be effective ways of removing the oil before it causes a reaction (26).

Beyond this ten minute window, rinsing the affected area and treating it with mild detergent is still advised as a first step treatment. According to the AAD it can help rinse off the urushiol oil to prevent spreading the rash to other areas of your body

The AAD also recommend washing your clothing, washing any other object that may have come into contact with the oil and that you avoid scratching at all costs!

Scratching can cause an infection or open blisters and expose raw skin. It may feel good in the short term but do not scratch that itch!

Home remedies and treatments

Scratching may be out but, fortunately, there are some home treatments that can help alleviate the discomfort of a urushiol rash.

• Short, lukewarm baths and short, cool showers can help soothe the aggravated area.
• The AAD also recommend applying a “cool compress,” such as a cloth soaked in cold water to the area to soothe it
• Reader’s Digest go a step further and suggest ten home remedies that can help soothe rashes. Lemon juice can help eliminate the urushiol oil, while apple cider vinegar can draw out the poison. Cooling substances like aloe vera, banana peels and even cucumbers can soothe the rash, while baking soda or oatmeal can be used (not at the same time!) to make pastes or symptom-reducing baths. Check out this link for details of exactly how to make use of these inventive remedies.

Medical remedies and treatments

It seems safe to say that most of us, faced with a bothersome rash, would rather head down to the pharmacy for a cream than walk around wearing slices of cucumber as a remedy! If you’re that kind of person you’re likely to find yourself discussing some of the below treatments with your pharmacist/doctor:

• Antihistamine pills can help soothe the itch but do not make the mistake of assuming antihistamine cream will do the same thing. It can spread the rash! (27)
• calamine lotion or hydrocortisone cream are the go to options if you wish to apply a cream directly to the rash (28)
• Your doctor/pharmacist may make other recommendations

Frequently Asked Questions

Can it kill you?

• According to USA Today urushiol can cause a deadly allergic reaction if consumed via a raw cashew, however there are no known cases of plant reactions causing death

Is it contagious?

• No. Contact with a rash will not spread the rash to another person. Only direct contact with urushiol oil can cause the reaction (29)

When poison ivy oozes is it healing?

• It is recommended that you see a doctor if your rash oozes pus – it can be a sign of complications rather than healing (30)

When does poison ivy have berries?

• In summer berries begin to grow. There may still be some on the tree as late as winter if they haven’t dropped off or been eaten by birds

Will it go away on it’s own?

• In most cases the rash will go away without treatment within a week or two (31)

When to see a doctor

• When suspected urushiol contact causes difficulty breathing, a severe, widespread rash, a rash that doesn’t go away in two weeks, blisters ooze pus or the rash affects the eyes, mouth or genitals (32)

Note: I’m not a doctor and this is not medical advice.