See if you know how to recognize poison ivy with this quiz.

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 annually.

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

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

Poison ivy, which produces urushiol throughout the plant, not just in the leaves, can cause year-round rashes.

Urushiol, the oily toxin in poison ivy, can remain allergenic on clothing for up to 5 years—or even longer.

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 was sent to Europe in the 1600s as an exotic, ornamental oddity.

Scientists testing how climate change affected plants found in a yearslong simulation study that poison ivy grew 70% faster than it did without extra carbon dioxide.

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.

In 1982, around 20% of the people who ate some of the roughly 7,400 bags of cashews sold as part of a Little League fundraiser in Pennsylvania broke out in rashes because of natural urushiol residue on the nuts' shells that hadn't been removed and fully cooked off—the same allergy-inducing substance found in poison ivy.

Plants use physical and chemical defenses to protect themselves

Tree bark is difficult to chew and resistant to pathogens, while the waxy cuticle on the surface of leaves deters insects and microbes. Some plants possess thorns, spines, and prickles to discourage predators. Plant cells can also produce antimicrobial toxins or release compounds to alert parasitic wasps to lay eggs in attacking insects.

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

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.

Some invasive plants, such as English ivy, maiden grass, and Norway maple, can swiftly take over gardens and damage yard structures if left unchecked.

Zoo animals have developed allergies, too

Although scientists do not know if allergies manifest among wild animals—and if animals can survive with them—in a zoo setting, veterinarians have observed zoo animals with common allergy symptoms, including itchiness, crusty skin, and runny eyes. Veterinarians have identified Asian elephants with pollen allergies and at least one jaguar with an allergy to fleas.

Natural toxins produced on plants or consumed by animals may cause food poisoning

When humans eat plants with certain natural toxins on them—including a family of toxins called aflatoxins that fungi produce on crops like peanuts and corn— they can become ill with food poisoning. Toxins can still harm humans even if animals or plants appear fine to the human eye. The World Health Organization advises that we should throw away moldy or discolored foods, refrain from eating wild plants or mushrooms that aren’t definitively nonpoisonous, and remember that just because something is “natural” it’s not always safe to eat.

The complexity of classifying a tree

It may seem obvious to us when we see a tree, but very specific characteristics cause scientists to distinguish trees from other types of plants. This video provides a visual and verbal explanation of distinctions that separate trees from other plants like shrubs or herbs. See a scientific breakdown of these traits.

See the differences between chickenpox and hand, foot, and mouth

This helpful explainer breaks down the differences between these two contagious, viral diseases, which both present with fevers and sores. It includes photos of the sores that are characteristic of both diseases, showing how they have appeared across different skin tones to better inform people looking for information about their own loved one's symptoms.

Allergy tests identify antibodies, but not whether allergy symptoms may appear

Skin prick tests and blood tests, the two most common allergy tests, both detect the presence of allergen-specific antibodies. But just because the body has those antibodies doesn’t mean that a person is “allergic” to a substance or that they will develop symptoms of an allergy when encountering the substance. Allergists work with families to interpret the results and sometimes combine that data with approaches including exposure challenges—giving someone a tiny bit of the food or substance they may be allergic to—under medical supervision.

What do psychedelic plants look like?

Far from the drippy aesthetic often associated with psychedelics, the plants powering naturally occurring psychoactive experiences may not stand out as anything special. This database offers a visual guide to psychoactive plants and fungi. Clicking on the title of a particular plant, such as yerba mate, will bring up a secondary screen with various hyperlinked images, such as the plant itself, related botanical drawings, and molecular structures.

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.

Explore Amazon rainforest species in this interactive

Explore plant and animal species from different parts of the rainforest, including the canopy, forest floor, and river basin while learning some general facts specific to the Amazon rainforest.

Test your ETF knowledge

A 10-question quiz from the SEC allows investors to test their basic knowledge about exchange-traded funds and their investing counterparts, mutual funds. Here’s a sample question: Is the past performance of a fund a good indicator of future results? (Hint, the answer is no).

See colorized mpox virus particles grown in culture at Fort Detrick, Maryland, where high-biosecurity pathogens are studied.

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

Test your ability to identify AI-generated images

This interactive project from MIT challenges users to distinguish between AI-generated images and real ones.

Photos and descriptions of unique plants found in the Amazon rainforest

It’s the plants that provide homes for the incredible diversity of Amazon animals. Read about 29 of the most fascinating Amazon rainforest plants.

The science of food allergies

Why do certain substances trigger an immune response while others don't? Listen to researchers explain the science in this five-minute video. Food allergies affect around 8% of children and 2% of adults in the US, and—unlike sensitivity or intolerance—they involve the immune system mistaking certain harmless proteins in foods as dangerous invaders, triggering a rapid and sometimes severe defense response.

Watch students comically portray how plants can detoxify the environment

Through a series of processes that collectively make up phytoremediation, plants can take up pollutants from soil and water through their roots, then break them down, release them as less harmful gases, or store them within their cells. Any plants that sequester heavy metals or other toxins must be removed and managed after the environment is decontaminated.

Test your emotional intelligence with this quiz

Emotional intelligence is the instinct and art of understanding feelings: both your own and those of others. Studies demonstrate people with high emotional intelligence often succeed in leadership positions, as they can better serve the real needs...

Why some people have allergies

Why do some people have allergies while others don’t? One theory suggests allergies are a relic of our evolutionary past. Our immune system, once primed to fight parasites, now mistakes harmless substances for threats.

Are you burned out? Take this quiz

Have you ever wondered if what you’re experiencing is burnout, or just stress? This Psychology Today quiz may help you decide if you need to explore more mental health resources. You don’t have to create an account to take the quiz. Simply answer the questions and provide your ZIP code.

Watch the safe way to remove a tick from your body

Minimizing your risk of Lyme and other tickborne diseases hinges on quickly removing ticks. To do so, place tweezers on the animal as close to the skin as possible and then pull directly upwards to try to avoid leaving bits of the tick's body behind. If possible, try to take a photo of the tick to share with your doctor to better identify potential disease risks (since certain tick species can carry specific diseases). Next, dispose of the tick without crushing it in your fingers—flushing it down the toilet, or placing it in alcohol or a sealed bag—and then thoroughly wash the bite area and your hands.

View a gallery of plants made to shine using ultraviolet-induced visible fluorescence photography, in which organisms re-emit the ultraviolet light they are exposed to in vibrant, glowing colors.

From glands beneath their skin, hippos produce their own sunscreen in the form of a fluid containing hipposudoric and norhipposudoric acids, which absorb sunlight in the ultraviolet and visible range.

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

Researchers are investigating if nanoparticle treatments could combat allergies

In rodent work, Northwestern University’s Evan Scott (now at the University of Virginia) and his colleagues have been trying to attack allergies with specially designed nanoparticles—miniscule lab-made objects that can penetrate cells. They stud the nanoparticles with a tiny bit of the allergen specific to the allergy (i.e. cashew protein for cashew allergy) and antibodies that shut down allergic response processes.

A visual database of pollens

Pollen is a powdery substance made up of small grains involved in the fertilization process of plants. There are thousands of types of pollens across the world, and you can see real images of them in this visual database.

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.

Explore guides on pollinator-friendly plants native to where you live

Pollinators have co-evolved alongside specific plants from their natural habitat and see their populations increase in environments with these native flora. This collection offers recommendations for regional plants that can provide nectar and pollen, serve as host plants for caterpillars, and offer nest sites for specialist bees.

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.

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.

Virtually all plants are biofluorescent because their photosynthesis is powered by chlorophyll, a pigment that glows red as a way to get rid of excess energy when exposed to ultraviolet light.

See examples of hyperaccumulators, the plants that can harvest heavy metals

These ideal species for phytoremediation possess biochemistry that allows them to absorb and store these elements without being poisoned by their accumulation. Pycnandra acuminata, one such plant, has blue-green sap due to an abundance of nickel, which it captures from the nickel-rich soil in which it grows.

Mineral and chemical sunscreens protect differently, but both guard against UV damage.

Take a quiz to identify whether you can spot deepfakes

Advances in artificial intelligence have made deepfakes increasingly difficult to identify, as they are intentionally designed to appear real. The technology has exacerbated some of the problems brought on by digital editing tools like Photoshop.

What is the rarest color in nature?

Plants, animals, or minerals found in nature bear almost every color imaginable. There are two factors that influence what hues you see in the wild: physics and evolution. So, which colors are you least likely to see in the natural world? Victoria Hwang explores one of nature's rarest spectacles.

See the incubation periods for certain food poisoning-causing organisms

Read this chart that lists common food sources of different foodborne illness-causing pathogens and typical times between exposure and symptom onset.

Infographic illustrates the diverse and fragile Amazon ecosystems

This infographic helps readers better understand the vast rivers, forests, plants, and animals that call the Amazon rainforest home. Home to the largest collection of plant and animal species in the world, the Amazon rainforest has 16 thousand known...