Leprosy affects the skin, eyes, and upper respiratory tract

Nerve axons become damaged by leprosy, so patients may lose feeling in their skin

Infection of the peripheral nerves—nerves outside the brain and spinal cord—is a known complication of leprosy. That damage can cause patients to lose their sense of touch and the ability to feel pain or temperature in affected areas, leading to accidental injury.

Leprosy doesn't cause fingers or toes to fall off

The nerve damage that results from infection sometimes causes loss of feeling in extremities so injuries like cuts or burns may be missed. In such cases, resulting infections can lead to digit loss. Fingers or toes can also appear to shorten with this disease because nerve damage can sometimes make muscles in fingers and toes so weak that they're reabsorbed by the body.

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.

Watch how doctors examine leprosy patients for signs of vision impairment

Clinicians must screen for symptoms of eye and vision damage in leprosy patients, including loss of sensation, reduced blink reflex, and inability to close or keep the eyes closed.

About 95% of people are naturally immune to leprosy

Contracting it requires prolonged contact with someone with the disease, meaning you'd have to be living with them. You cannot get leprosy from hugging someone with leprosy or sitting next to them. It's not known to pass from mother to fetus. The risk of transmission from armadillos is also likely low, but people should avoid touching wild animals for general safety.

More than 200,000 people are diagnosed with leprosy annually

The disease still occurs in more than 120 countries. Brazil, India, and Indonesia continue to report more than 10,000 new cases annually.

See examples of leprosy in the Bible—a broad term for skin ailments in ancient times

People afflicted with leprosy in the Bible may have had a range of different skin diseases, rather than what's clinically diagnosed as Hansen's disease (leprosy) today. In the Bible, as in many traditional societies, those with the disease were often considered unclean or sinful.

Leprosy bacteria are sometimes grown on mouse feet for research

The main leprosy-causing bacterium can't be grown in a petri dish, so the disease is challenging to study in the lab. For research purposes, it has been grown in the foot pads of mice.

America had a national leprosarium—a leper colony—in Louisiana until 1999

Public health officials forcibly sent those diagnosed with leprosy to the Louisiana Leper Home in Carville, first founded in 1894. Listen to an interview about this site, its evolution, and how its residents advocated for themselves—including regaining the right to vote.

Recent research indicates leprosy was present in the Americas before European settlers

New research published in 2025 upended long-held notions that the disease was introduced to the Americas by European colonizers. Evidence of a lesser-known leprosy-causing bacterium was found in ancient human remains that date back 4,000 years.

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.)

Lyme disease is caused by bacteria transmitted through the bite of infected ticks

It's an infectious disease caused by Borrelia burgdorferi bacteria. It's spread through the bite of two species of infected ticks, the Western blacklegged ticks on the West Coast, and Blacklegged ticks found throughout the eastern US. The ticks can transmit the disease at both the nymph and adult stage. It's not known to be transmitted from one person to another via kissing or sex.

Rabies is nearly 100% fatal once symptoms appear

Rabies, a viral disease attacking the central nervous system, is nearly always fatal once symptoms appear. It spreads through the infected animal saliva (typically through bites) and causes encephalitis, leading to severe neurological symptoms and death. See how the lyssavirus—the bugs behind rabies—work once inside the body.

Lupus, an autoimmune disease with varied symptoms, was named for wolf bite-like lesions

The 13th-century physician behind the name (lupus is Latin for wolf) named it after a patient he saw who had facial lesions that looked to him like a wolf's bite. Other common symptoms of the disease include extreme fatigue, painful and swollen joints, fevers, and light sensitivity.

Hand, foot, and mouth disease spreads easily—including via fomites

The common ailment spreads through respiratory droplets, touching infected secretions like poop, but also by touching virus-laden fomites, which are contaminated objects such as doorknobs or toys.

Secondary complications from measles in children range across the whole body

The most serious effects of a measles infection, particularly in young children, come from its attack on the immune system. This leaves the whole body vulnerable to follow-on diseases, with some of the most serious including respiratory conditions, encephalitis, and more.

In 2011, a mysterious illness spread around LeRoy, New York

A handful of girls were stricken with bizarre twitches, tics, and spasms — all apparently involuntary. Some believed the incident to be conversion disorder, an illness where emotional troubles have physical symptoms.

Cryptococcus neoformans, a growing threat, causes infections in the brain and lungs

This inhalable, microscopic pathogen is found worldwide. It rarely causes illness, but it can take root in those with compromised immune systems, including people with advanced HIV/AIDS. Symptoms of cryptococcal infection—such as a stiff neck, vomiting, and confusion—can begin weeks or months after breathing in spores, though sometimes symptoms won’t appear for years. There are no known cases of transmission between people or between people and animals.

Treating black fever can result in a complication that spreads the deadly disease

Black fever, a deadly parasitic disease second only to malaria, threatens more than 1 billion people across more than 83 countries. Also known as kala-azar or visceral leishmaniasis, the disease is caused by parasites that spread through sandfly...

How ALS (Lou Gehrig’s Disease) might work, and what scientists are learning about it

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder that affects the nerve cells (neurons) controlling muscle movement. As the motor neurons degenerate, they stop sending signals to the muscles, causing progressive muscle weakness and, eventually, death. This three-minute animation focuses on the mechanisms within the motor neurons that cause them to degenerate. By understanding these mechanisms, researchers hope to one day find a cure for ALS.

Herpangina is a related disease that also has characteristic sores in the mouth and throat

This painful condition is also caused by several viruses in the enterovirus family. The condition typically has early symptoms including a fever and sore throat, in addition to the sores. Herpangina is often mistaken for strep throat, but there's no cure for herpangina and patients typically have symptoms for about a week.

Sclerosis is the technical term for the lesions or plaques that form without myelin

In the absence of myelin, the body forms scar tissue called sclerosis. That scar tissue hampers nerve's abilities to transmit nerve impulses, essentially acting as a roadblock to speedy communication.

Usher Syndrome, a rare genetic disorder, causes progressive hearing and vision loss

People with one of the subtypes of this condition have a genetic mutation that starves cells in the inner ear and the retina of proteins required for detecting sound and light. Gene therapy in animals has seemed like a promising treatment for the condition.

The resurgence of Black lung disease in coal miners

Black lung disease is a preventable condition long associated with coal miners who regularly breathe in toxic coal dust. Simple workplace safety procedures make the disease entirely preventable, but cases are rising. Due to lax enforcement of rules, miners in Central Appalachia are increasingly diagnosed with cases stemming from silica dust inhalation.

Watch what the Ebola virus does inside our cells and organs in order to spread and survive.

Scleroderma, which causes skin to harden and scar, has no FDA-approved treatment

It's an autoimmune disease that disproportionately causes worse complications in African American people for unknown reasons. It causes the body to overproduce collagen after the immune system attacks the body's own connective tissue, leading to excess collagen deposits and restricted blood circulation as small blood vessels are damaged. It can damage various organs, including the lungs.

About 2,000 US babies are born annually without some portion of their limbs, potentially leading to a lifetime of pricey prosthetics.

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.

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

See images of medical cases of firework injuries shared on this 'Instagram for doctors.' (Warning: Graphic content)

The concept of phantom limbs, the perception that amputated limbs are still present, dates back to a French military surgeon in the 16th century.

In 1939, baseball star Lou Gehrig delivered his inspirational 'Luckiest Man' speech after retiring due to the health condition that now bears his name.

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

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

Fear or disgust related to clusters of holes and cracks, called trypophobia, may stem from evolutionary processes to help us avoid pathogens.

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

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

The first line of 'immortal' human cells, which can divide indefinitely and are used in scientific research, was nonconsensually taken from a Black woman.

Planarian flatworms are small, aquatic worms with exceptional regenerative capabilities. When cut, the worms can regenerate multiple bodies in a matter of weeks.

Radioactive elements can introduce software errors because the ionizing radiation they produce can detach electrons from atoms, and computer code relies on the distribution of electrons.

Alzheimer's can lead to brain shrinkage, with an average of around 2% of volume reduction per year

In 2019, a laptop loaded with six of the worst malware in history and described as 'an exhibit of historical weaponry' sold for $1.3M.

The hormonal disorder PCOS was renamed PMOS in 2026, a move designed to improve care and research by shifting the focus to the hormonal causes of this condition that affects 1 in 8 women.

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.

The American cockroach is actually from Africa, an apparent hitchhiker aboard ships carrying enslaved people, with evidence suggesting the bug may have arrived in the New World as early as the 1600s.

The deadliest aspect of volcanic eruptions is often not lava, but pyroclastic flows—avalanches of ash, gas, and rock that can move more than half the speed of sound.

While El Niño moves warm Pacific Ocean waters east along the equator, La Niña moves them west, shifting where rainfall will become more common for months.

The Great Salt Lake's distinct dual coloration results from high-salinity organisms that only live in the northern portion and produce a purple protein.

In 2018, 26-year-old missionary John Allen Chau was killed by tribesmen after attempting to reach and evangelize on India's isolated North Sentinel Island

Explore the known asteroids, comets, and spacecraft involved in asteroid studies within our solar system with 'Eyes on Asteroids,' a 3D visualization from NASA.