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

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.

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

Poison ivy can cause rashes any time of the year

This myth-busting article about poison ivy notes that all parts of the plant contain urushiol, the oil that triggers our allergic response, so if you are in the woods in winter you may be still encounter the plant—and urushiol.

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.

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

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.

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.

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

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.

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

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.

Volatile chemical contamination can last in burn areas long after urban wildfires

Lead, arsenic, asbestos, and other chemicals have been found trapped in smoke-exposed rugs, couches, pillows, and other furniture that appeared otherwise undamaged from the 2025 LA wildfires. The gradual release of these substances has produced dangerous indoor air concentrations and contributed to increased emergency room visits and abnormal blood tests.

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.

Wearing tick repellent, covering up, and performing tick checks are the best Lyme prevention

Spraying repellents onto your clothes—and reapplying them—or donning impregnated bug-repelling clothes can help keep ticks away. Effective sprays include DEET, picaridin, or permethrin. Bug spray applied to the body should be applied on top of sunscreen, and only after the sunscreen has dried.

Leprosy symptoms may appear 20 years after infection, so contact tracing isn't possible

The standard approach for tracking disease transmission isn't realistic for this disease because symptoms may take decades to manifest. As a result, disease transmission is still not fully understood.

Skin wounds and burns heal fastest if they occur during the day

Skin cells responsible for healing wounds work more quickly during the daytime, underscoring that the timing of an injury greatly influences recovery time, according to 2017 research. Nighttime burns took an average of 11 days longer to heal than burns incurred during the day. (Some readers may experience a paywall.)

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.

Knowing how to use an EpiPen is a life-saving skill—learn how with this video

If someone has a severe allergic response, including trouble breathing or two or more allergic symptoms, it may be necessary to administer epinephrine, usually through an injection. Epinephrine autoinjectors—often called EpiPens—should be injected into the mid-outer thigh, even through clothing, for about 10 seconds, depending on brand. Sometimes another injection with a separate EpiPen is required if the patient does not get better after a few minutes.

Short-term cortisol spikes can boost the immune system

Elevated acute levels can enhance the immune system's ability to fight off infection or respond to injury. Chronic heightened cortisol levels, however, can lead to inflammation that harms cells and tissues over time.

We can get food poisoning from spending time in swimming pools, lakes, rivers, and ponds

Some of the same pathogens that may sicken us in food or water may also sicken us in recreational swimming environments. Bacteria can rub off of people’s (or animal’s) bodies or contaminate the water through a diarrheal episode. Washing your hands for at least 20 seconds before eating food if you are at the beach, pool, or other similar environments and being sure not to swallow the water are ways to help keep safe.

Home allergy tests don’t work well and experts urge caution

Doctors do not recommend at-home allergy test kits because their results may be inaccurate and confusing, and lead people to make lifestyle changes that are not warranted. Tests that require sending in a hair sample, for example, will not be helpful because hair does not have the relevant antibodies that blood testing would detect.

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.

Watch the cumbersome, but necessary, precautions healthcare workers must take to care for and protect themselves while caring for Ebola patients

Treating someone with Ebola involves a painstaking process of suiting up (donning) and peeling off (doffing) protective gear. Doctors follow detailed CDC guidelines. Properly suiting up is key to protecting against fluids that transmit Ebola, and correctly removing a suit that could be contaminated with the virus is also critical.

Shingles vaccine may slow biological aging in older adults

Research published in 2025 that analyzed data from thousands of older adults found that those who had received the shingles vaccine exhibited signs of slower biological aging, such as lower levels of inflammation and slower epigenetic aging, than those who had not been vaccinated.

Watch the cumbersome, but necessary, precautions healthcare workers must take to care for and protect themselves while caring for Ebola patients.

The UV index measures the sun's ultraviolet radiation risk on a scale of 1 to 11+

The tool takes into account geographical location, time, elevation, and cloud coverage to help individuals plan their daily activities around the sun's peak UV exposure times, which occur from 10:00 am to 4:00 pm. A value at or above 6 requires sunscreen (SPF 15+), shelter, or UPF clothing

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.

Heat-related complications are of greater concern for distance runners than cardiac threats

Analysis of more than 130,000 runners in Tel Aviv events during a seven-year period indicated that the runners were 10 times more likely to experience heatstroke than serious cardiac problems. Scientists suggest that runners should take 10 to 14 days to acclimate to a hot climate before tackling a serious run.

Understanding the causes and environmental impacts of crude oil spills and leaks

Although some oil regularly leaks from the bottom of the oceans through the gradual erosion of sedimentary rock, major spills result from accidental ruptures of pipelines or damage to transportation vessels or rigs. Oil can break down the water-repelling ability of feathers, remove the insulation of fur, and poison food chains if ingested.

Human-to-human transmission of hantavirus remains extremely rare, so the 2026 hantavirus cruise ship outbreak doesn't mean we're facing a COVID-style pandemic risk.

Firework or sparkler burns, even if they cover a relatively small area of skin, can significantly affect our range of motion.

There is no cure for the general condition of arthritis

While there are innumerable conditions ultimately leading to the joint pain we collectively term "arthritis," one common pathway is progressive inflammation and joint damage many years after an injury.

Tattoos remain visible on your skin thanks to immune cells called macrophages

About 12.5% of US adults experience a phobia in their lifetime, a diagnosis that hinges on the intense fear interfering with daily life and persisting for at least six months.

When a Paris department store hesitated to sell Estée Lauder's perfume, she 'accidentally' broke a bottle, causing the smell to spread throughout the store and shoppers to start asking to buy the scent.

Read a deep dive on the 'all-purpose healing' peptide BPC-157.

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

To reduce wrinkles in clothing, research recommends gentle wash cycles with more water and tumble drying with smaller loads and longer times.

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.

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

Volcanoes 'die' when their supply of magma runs out, if they are shifted away from their underlying magma reservoir, or if they get clogged by collapsing or their magma cooling back into rock.

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.

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.

The US first hosted the World Cup in 1994, a tournament that lives in soccer infamy for its poor planning and the murder of Colombian player Andres Escobar, who'd accidentally scored on his own net.