Even dead leaves, stems, or roots contain the oil; it can also be inhaled if the plants are burned. Urushiol is the same oil that is produced by poison ivy and sumac.
Alternatively, indirect contact can occur if the oil gets onto clothes or is carried on a pet's coat. Although cats and dogs are not generally affected by urushiol, they can carry it.
Most people, but not all, show an allergy to the oil, referred to as allergic contact dermatitis. It usually appears between half a day and 3 days after contact with the plant oil.
People who are allergic to the oil do not have a reaction until they have a second contact with the oil. The immune system learns to recognize the oil from the first occasion and then reacts to it aggressively on future contact.
According to the Centers for Disease Control and Prevention (CDC), most people are sensitive to the oil in poison oak, ivy, and sumac:
"When exposed to 50 micrograms of [the oil], an amount that is less than one grain of table salt, 80 to 90 percent of adults will develop a rash."
What does poison oak rash look like?
Poison oak rash.
Image credit: Britannic124
A poison oak rash appears where the contact with the oil occurred. However, it can also form on parts of the body not contacted by the plant.
It normally starts as itching and mild irritation and gradually worsens developing in to a red rash that gradually gets more itchy.
Bumps will form, which can turn into blisters.
The rash gradually resolves over a period of 3-4 weeks.
The irritation varies depending on which area is affected, but some features are common anywhere on the body:
Blistering poison oak rash, showing the classic linear pattern.
Image credit: CDC
- It always involves intensely itchy, red skin.
- Often there are multiple streaks in the area of skin brushed by the oil.
- Swelling is common, sometimes hives can appear.
If there is a large area affected by the rash, or it is in a place that makes movement difficult, the problem is more serious. This is most commonly the case for people who are often exposed to the plants, such as those working where poison oak grows.
The rash should quickly settle down and begin healing; but it can take a few weeks for a poison oak rash to clear up fully.
The rash itself cannot be spread between people. However, anyone who is regularly exposed should be careful to avoid spreading the oil and causing a reaction in other people; for instance, if the poison oak oil is transferred from protective gear, clothes, and tools.
Any swelling beyond small hives in the affected area should visit a doctor. For anyone who has a wider reaction, it is important to get medical help.
People should call for immediate medical help or go to an emergency room straight away if any reaction causes these signs of severe allergy:
- swelling around the eyes, face, lips, or tongue
- any effect at all on swallowing or breathing
- a strong feeling of being unwell
- signs of infection, such as spreading redness, pus, or pain
- swollen lymph nodes
What does poison oak look like?
Recognizing the actual plant itself is tricky because individual poison oaks come in different forms. Below are some examples:
Poison oak grows wild as a woody shrub if it gets full sun, or as a climbing vine in the shade of woods. It is mostly found in forests and woodlands, fields, or open land with shrubby areas. It can also thrive at roadsides and on abandoned land.
Poison oak is native to the western United States and can be seen anywhere across North America, except Alaska. It is a bigger problem in the coastal regions of the southeast and the west.
Poison oak has leaves that usually come in threes. Sometimes, though, there are five, seven, or nine leaves in a group. These leaves are absent in winter.
Other keys to identifying poison oak are:
- Poison oak does not look like true oak - true oak has single leaves that do not group together in patterns of odd numbers.
- It has leaf groups, usually in threes, that alternate along each side of the stems.
- It has only one group of leaves coming off at one point on a stem, and then another on the opposite side of the stem further up - and so on.
Image credit: Eeekster
Poison oak during its flowering phase.
Image credit Noah Elhardt
This is an example of the berries found on poison oak.
Image credit: Gregg Erickson
The leaves can be glossy or dull, and sometimes hairy underneath. Poison oaks are varied:
- The leaves come in different sizes on various plants - 1-4 inches long.
- The leaves in each of the groupings on the stems are similar in size, although the middle leaf is often longer.
- Leaf edges can be toothed or lobed.
If a person thinks they have come into contact with poison oak, they should wash their skin and clothes in warm, soapy water as soon as possible.
The allergic rash should start to settle down naturally. Ways to soothe the rash and prevent it from getting worse include:
- Staying away from the poison oak and keeping the rash from getting irritated or infected by anything else.
- Not scratching at the itch as this can cause more damage, itchiness, pain, and infection.
- Simple, clean, warm water bathing, followed by clean, dry, gentle patting or natural drying helps.
- Using emollient cream to protect the skin from losing moisture and keep the skin's barrier function. Emollient cream is available for purchase online.
Antihistamines, like diphenhydramine, can ease the itchiness. A range of antihistamines is available for purchase over the counter or online.
However, it can also make people drowsy, so it should not be taken before operating heavy machinery or driving.
People should see a doctor if:
- the rash does not go away within 3 to 4 weeks
- symptoms get worse
A doctor can prescribe oral or topical steroids or stronger prescription antihistamines.
The easiest advice for avoiding poison oak and the nasty rash it can cause is to:
- Know where the plants are and avoid them.
- Know that the oil is released by damage to the plant.
- For unknown plants, look out for the leaf-group pattern of poison oak.
- If a pet is thought to have contacted poison oak, wash it thoroughly.
- Do not burn poison oak as the oil can be inhaled and cause internal damage.
Poison oak at work
People whose work puts them at a higher risk of contact with poison oak oil need to take measures to protect themselves. Employers must also help.
The National Institute for Occupational Safety and Health (NIOSH) have detailed some good tips for workers with a fact sheet on poisonous plants.
The following video from NIOSH shows why the skin reacts to poisons that cause allergy. NIOSH have used animated drawings to simplify the way the immune cells of the body react to poison oak and produce the rash: