Poison ivy can cause rashes year-round since all parts of the plant contain urushiol, the oil that triggers our allergic response.

Poison ivy's rash-causing compound is found in the plant's roots, stem, and leaves—so coming into contact with any part of the plant can lead to rashes for the 85% of people who are allergic to it.

Poison ivy's characteristic rash is caused by an allergic response to an oily compound in the plant called urushiol.

Poison ivy's characteristic rash is caused by an allergic response to an oily compound in the plant called urushiol.

Urushiol, the oily toxin in poison ivy, can remain allergenic on clothing for years.

Poison ivy's rash-causing compound is found in the plant's roots, stem, and leaves—so coming into contact with any part of the plant can lead to rashes for the 85% of people who are allergic to it

Once sold as an ornamental plant, poison ivy can actually look varied—its colors change seasonally from reddish to green to yellow. It typically has three broad, shiny, tear-shaped leaves. But it sometimes may have a different number of leaves, and its edges can be serrated.

Urushiol, the oily toxin in poison ivy, can remain allergenic on clothing for years

The substance can still cause rashes even after being on shoelaces, clothing, sleeping bags, boots, or other clothing for multiple years—some reports say five years on surfaces—so they all need to be washed after outdoor adventures with the plants.

Between 10 million and 50 million people in the US develop rashes from poison ivy, poison sumac, and poison oak each year.

Poison ivy's characteristic rash is caused by an allergic response to an oily compound in the plant called urushiol

Chinese lacquer tree sap also contains urushiol, yet the sap was widely used as a lacquer in Asian lacquerware for thousands of years. The word "urushiol" is derived from the Japanese word "usushi," which is the word for the lacquer tree.

Poison ivy is projected to be larger and more resilient due to climate change

Elevated atmospheric carbon dioxide boosts the growth rate of the plant and the resulting leaf area. These larger plants contain more uroshiol—the substance most humans are allergic to—and are hardier, recovering from damage more quickly than their smaller counterparts.

Poison ivy is in the same family as mangoes, cashews, and pistachios—and they all produce oily urushiol in their raw, unprocessed state—but they are typically prepared in ways to avoid causing human discomfort.

Poison ivy will likely become both larger and more resilient due to climate change.

This poison ivy knowledge quiz—accompanied by photos of the plant's varied forms—may help you identify this common rash-inducing growth.

Between 10 million and 50 million people in the US develop rashes from poison ivy, poison sumac, and poison oak annually

If someone is exposed to one of these plants for the first time, it can take several weeks to develop a rash.

See if you know how to recognize poison ivy

This quiz, accompanied by photos of the varied forms of the plant, may help you identify the plant when it counts.

Poison ivy is in the same family as mangoes, cashews, and pistachios—and they all produce oily urushiol in their raw unprocessed state, and chewing mango skin can produce blister rashes

Poison ivy only seems to lead to allergic responses in humans, other primates, and guinea pigs. Other animals can both interact with the plant and eat it without becoming sickened.

Poison ivy was sent to Europe in the 1600s as an exotic, ornamental oddity, where it was purposefully grown in the English royal gardens at Kew, the Faculty of Medicine in Paris, and a few other locations.

During the French Revolution, a botanist's letter asking about "dear Rhus" (poison ivy) was intercepted and led to authorities' suspicions he was conspiring with the Russians

The 1794 incident involved André-Ignace-Joseph Dufresnoy, a French army physician researching the plants' potential medicinal properties. Rhus radicans is a scientific name for the plant, though it's commonly called Toxicodendron radicans.

You can be allergic to grass—but there are other reasons it can make you itch

Seasonal allergies don't always show up in childhood

The human immune system may become sensitized to pollen and develop an allergic reaction to it after prolonged exposure. Other triggers for new seasonal allergies may include exposure to new environments and changing climate conditions that affect allergy season length and conditions for various pollens.

During the French Revolution, a botanist's letter asking about "dear Rhus" (poison ivy) was intercepted, leading authorities to suspect he was conspiring with the Russians.

Allergies occur when our immune system mistakenly considers a substance a threat

Immunoglobulin E antibodies, or IgE antibodies, may bind to an allergen, effectively labeling it as a threat. That triggers a cascade of actions in the body, including the release of histamine, which causes the characteristic itching and hives of allergies. Sometimes a cooked version of an allergen—like a cooked carrot—may look different enough from its raw form to the immune system that antibodies ignore it, and no allergic response takes place.

Hand, foot, and mouth is usually seasonal—peaking in summer—but not always

This painful, contagious disease most commonly has outbreaks in summer and early fall in the US because the enteroviruses that cause disease can most readily survive and be transmitted in warmer, humid conditions. It can still show up throughout the year, however.

Erythema migrans rash is common in Lyme—but it often doesn't look like a bull's-eye

The US Centers for Disease Control and Prevention states that this rash occurs in roughly 70% or more of Lyme disease patients, and typically occurs at the site of a tick bite. The rash may expand slowly over several days and feel warm to the touch, but it's rarely itchy or painful. As it grows, areas of it may clear—creating a target or "bull's-eye" appearance.

Many patients with psoriasis develop other autoimmune diseases, too

A small study published in 2024 found that nearly three-quarters of patients with psoriasis—a condition in which the body attacks healthy skin cells—also developed autoimmune disorders including thyroid diseases, connective tissue diseases, and more, suggesting such connections between these autoimmune disorders warrant further exploration.

Demystifying sunscreen

Sunscreen is helpful all year round. Experts argue a minimum level of protection is SPF 30. There are two kinds of sunscreen: mineral (a physical barrier) and chemical (absorbs UV light). No new sunscreen ingredients have been approved in the US in decades, so foreign products are common.

Overuse of opioids can lead to hypersensitivity to pain

Opioid misuse can lead opioid-induced hyperalgesia, where the body becomes increasingly sensitive to pain. The body produces its own opioids as a way to temporarily block pain signals. When met with external opioid use, the body ratchets up pain sensitivity to ensure it senses the pain necessary to trigger its own response.

Beyond burns, fireworks can harm respiratory, auditory, and visual health

While mishandling fireworks can cause severe burns and loss of appendages, there are also risks for viewers of displays. Released particulate matter can cause the surrounding air to resemble wildfire smoke, and the explosions can cause hearing loss and damage to the corneas.

Leprosy has been detected in British red squirrels

The animals have been infected with both strains of the bacterium that cause leprosy. Researchers have found that squirrels living in different parts of the UK were infected with different species of the disease-causing bacteria. (Some users may experience a paywall.)

Do trees feel pain?

Trees don’t have nerves or brains. But when they’re wounded, they send underground and airborne warnings to other trees.

Ear infections can arise from chlorinated water, too

Any water remaining in the ear can lead to swimmer's ear. Chlorinated water, however, can also strip the skin of the oils and wax that would otherwise protect the ear.

Cold-blooded reptiles seek heat, and that behavior may help combat fungal infections

This Radiolab podcast episode takes on the idea that though our human bodies are too warm for the majority of fungal species to effectively replicate inside our bodies, that's not the case for reptiles. Yet when those species warm their bodies by basking in the sun on rocks, they can soak up heat and may also help keep fungal infections in check.

Scientists have unraveled new details about which nerve cells control goose bumps

Research in 2016 revealed that at least eight different types of neurons are associated with the sympathetic nervous system. One finding revealed that goose bumps and nipple erection are caused by neurons specialized to regulate these specific functions by controlling the erectile muscles in those tissues.

There's no definitive test for inflammation, or a baseline for what's considered normal

Existing tests can pick up proteins that indicate an immune response—in particular C-reactive protein, which the liver produces when the body's stressed—but that won't tell you why there's inflammation nor if it's chronic or acute inflammation. (Some users may experience a paywall.)

Protecting yourself from West Nile involves avoiding getting bites and clearing standing water

The best prevention against West Nile is avoiding getting bit. That means covering your arms and legs with long, loose-fitting clothes, wearing insect repellant—on top of, not under sunscreen, and making your environment as inhospitable to mosquitoes as possible, including clearing any standing water.

Certain vaccinations may be more effective when given around the middle of the day

A 2023 analysis of the health records of more than 1.5 million people in Israel suggests that COVID-19 vaccines may be more effective when received around the middle of the day. Separate early research also suggests there may be similar trends for influenza vaccines.

Fireworks-related ER visits are on the rise—in 2024, they increased by 52% as compared to the prior year.

An investigation suggests a Scottish island became awash in forever chemicals via seafoam and seaspray—raising questions about what that means for the safety of other coastal areas.

Listen to an in-depth conversation on the links between Parkinson's disease and herbicide exposure and the challenging pace of scientific investigation.

Louisiana's 'Cancer Alley' is infamous for having some of the highest industrial pollution, toxic air emissions, and cancer risks in the US.

Hookworm infection, though risky, may help fight certain autoimmune conditions by tamping down the immune system's inflammatory response.

An Ebola vaccine was developed during the 2018 west African Ebola outbreak, but the 2026 Ebola outbreak is with a different species of the virus, not the one that the vaccine is approved to treat.

Some renewable energy sources may weaken the resiliency of electric grids by removing outage buffers provided by coal- and natural gas-fired plants, which provide the system with more time to find a new power source if a plant goes down.

All rainbows are 'raincircles' caused by water droplets separating white sunlight into a spectrum of colors, but Earth's surface blocks the bottom half of the circle from our line of sight.

Animal phobias are likely the most common type of phobias, followed by an extreme fear of heights.

Sunflowers have long been a symbol of nuclear disarmament because they can extract large amounts of radioactive cesium from soil.

Before writing 'Walden,' transcendentalist Henry David Thoreau nearly burned down his hometown with a campfire that grew out of control.

Prince's sexually explicit 1984 track 'Darling Nikki' attracted the ire of the Parents Music Resource Center, an advocacy group that inspired the Parental Advisory sticker, even though the song ends with a Christian message.

Up to a million Girl Scouts sell about 200 million cookie boxes every spring, generating $800 million, largely because refusing a child is frowned upon

While the sun's gravity keeps the planets in orbit, their gravity also pulls on the sun, causing it and everything else in the solar system to orbit around a mutual balance point called the barycenter—the true center of the solar system.

The Russia-Ukraine conflict is the largest ground war in Europe since World War II in terms of casualties, forces mobilized, and displacement of civilians.