Hot springs and the brain-eating amoeba: how rare it is, and the one rule that matters
Naegleria fowleri lives in warm fresh water, hot springs included, and infects only through the nose. The CDC counts 167 US cases since 1962. Here is what that means for a soak, and the precautions that work.
Short answer: The risk is real but very rare. Naegleria fowleri, often called the brain-eating amoeba, lives in warm fresh water, hot springs included, and infects people only when water goes up the nose. The CDC counts 167 US cases of the brain infection it causes between 1962 and 2024, typically fewer than 10 a year, and only four survivors. You cannot get it by swallowing water or from another person. The CDC’s rule for hot springs is simple: always keep your head above water.
Hot springs are on the CDC’s short list of places the amoeba lives. The facts behind that are short, and they point to one habit that matters far more than anything else.
This guide sets out what the CDC says about how infection happens, how rare it is, and what to do at a hot spring, with the other hot spring hazards the National Park Service warns about.
This is general information, not medical advice. If you have symptoms after swimming or soaking in fresh water, get medical help right away, as the CDC advises.
What Naegleria fowleri is
The CDC describes Naegleria fowleri as “a free-living ameba, a kind of one-celled organism that thrives in warm freshwater lakes, rivers, and hot springs.” It is often called the brain-eating ameba because it can infect the brain and destroy brain tissue.
The infection it causes is called primary amebic meningoencephalitis, or PAM. The CDC calls these brain infections “very rare but nearly always fatal.”
The ameba lives naturally in the environment. Besides lakes, rivers, ponds and their sediment, the CDC lists “naturally hot (geothermal) water like hot springs or hot sources of drinking water,” along with poorly maintained pools and splash pads, tap water and water heaters.
How people get infected
Only one route matters: up the nose. If water containing the ameba goes up the nose and reaches the brain, it can cause PAM, the CDC explains.
Just as important is what does not cause it. The CDC says you cannot get PAM from:
- Swallowing water containing the ameba.
- Swimming or playing in a properly cleaned, maintained and disinfected pool.
- Another person: infections do not spread from person to person or cause outbreaks.
It adds that there is no evidence the ameba spreads through water vapor or aerosol droplets, such as shower mist or a humidifier. So the steam over a hot spring is not the concern; water up the nose is.
How rare it is
Very. The CDC says that typically fewer than 10 people a year in the US get PAM, and that between 1962 and 2024 there were 167 reported cases in the country. Only four people survived.
Most people who got PAM in the US were young boys. The CDC says the reasons are not clear, and suggests boys may be more likely to dive into water and play in the sediment at the bottom of lakes and rivers.
Most infections have been linked to swimming in southern states. Since 2010, though, the CDC says infections have been confirmed in Nebraska, Iowa, Minnesota, Indiana, Maryland and northern California, and it notes that rising water temperatures may be a contributing factor.
When the risk is higher
In lakes and rivers, timing matters. The CDC says infections usually follow swimming or diving in fresh water during summer months, and often happen when it has been hot for long periods, which raises water temperatures and lowers water levels.
A hot spring is warm by nature, so the CDC’s advice for hot springs does not depend on the season. Its guidance is to take precautions every time you go into a lake, hot spring or other warm fresh water, and it says it is safest to assume you can get the infection anytime you go into fresh water.
The precautions that work
The CDC’s list is short, and every item is about keeping water out of your nose.
- Always keep your head above water in hot springs. This is the CDC’s specific rule for springs. No dunking, no dives, no putting your face under.
- Hold your nose or wear a nose clip if you jump or dive into fresh water.
- Do not dig in shallow water, where the ameba is more likely to live.
- Rinse sinuses only with distilled or boiled water, never with water from a spring or a tap you have not treated.
The CDC says properly cleaned, maintained and disinfected pools do not cause PAM, so at a developed resort it is worth asking how the pools are treated. Primitive pools are untreated natural water, which is where the head rule matters most. Our guide to US hot springs explains the difference.
Symptoms, and what to do
The CDC’s symptom page says early symptoms can include a headache and fever, and that they can develop quickly. Its overview lists headache, fever, nausea and vomiting early on, then a stiff neck, confusion, loss of balance and hallucinations as PAM progresses.
The disease moves fast: the CDC says most people with PAM die within 1 to 18 days after symptoms begin. Its advice is to get medical help right away if you or someone you know has symptoms.
Kids at hot springs
The CDC’s case data skews young: most US cases were young boys, possibly because of diving and playing in sediment. At a hot spring, the head-above-water rule is hardest for children to keep, so it needs an adult watching.
Heat is the other concern for children. Our guide to saunas, hot tubs and cold plunges for kids covers the age limits and the CDC’s hot tub rule for young children.
The other hot spring hazards
The amoeba is the rarest danger at a hot spring, not the only one.
Scalding water. At Hot Springs National Park, the National Park Service says the thermal water emerges at an average of 143°F (62°C). Test the water before you get in.
Thin ground. At Yellowstone, the park’s safety page warns that the ground around thermal features can be a thin crust over super-heated water. It tells visitors to stay on boardwalks, not to touch thermal features or runoff, and states that swimming or soaking in hot springs there is prohibited.
Pregnancy. Hot water raises core temperature, and the guidance on hot tubs in early pregnancy is to stay out. Our guide to hot springs while pregnant covers it.
The amoeba and hot springs at a glance
| Question | What the CDC and the NPS say |
|---|---|
| Where it lives | Warm freshwater lakes, rivers, ponds and hot springs, and their sediment |
| How it infects | Water going up the nose and reaching the brain |
| Not from | Swallowing water, other people, properly maintained pools; no evidence for vapor or mist |
| How rare | Typically fewer than 10 US cases a year; 167 from 1962 to 2024 |
| Survival | Only four of those 167 survived |
| The hot spring rule | Always keep your head above water |
| Early symptoms | Headache, fever, nausea, vomiting; get medical help right away |
| Yellowstone | Swimming or soaking in hot springs is prohibited |
FAQ: hot springs and the brain-eating amoeba
Can you get a brain-eating amoeba from a hot spring? Yes, but it is very rare. The CDC lists hot springs among the warm fresh waters where Naegleria fowleri lives, and it infects only when water goes up the nose. Typically fewer than 10 people a year in the US get the infection.
How common is the brain-eating amoeba in the US? The CDC counts 167 reported cases of the brain infection it causes from 1962 to 2024, typically fewer than 10 a year. Only four people survived.
Can you get it by swallowing hot spring water? No. The CDC says you cannot get the infection from swallowing water containing the ameba. It enters through the nose.
How do you stay safe from the amoeba at a hot spring? Keep your head above water, which is the CDC’s specific rule for hot springs. Hold your nose or use a nose clip if you jump into fresh water, do not dig in shallow sediment, and rinse your sinuses only with distilled or boiled water.
Can the steam from a hot spring carry the amoeba? The CDC says there is no evidence that it spreads through water vapor or aerosol droplets, such as shower mist or vapor from a humidifier.
What are the symptoms of the brain-eating amoeba? Early symptoms can include headache, fever, nausea and vomiting, and they progress quickly to a stiff neck, confusion and loss of balance. Get medical help right away, as the CDC advises.
The bottom line on hot springs and the amoeba
The brain-eating amoeba is frightening because it is nearly always fatal, and reassuring because it is very rare and has one route in. Water up the nose is the whole risk.
Keep your head above water at every hot spring, keep children’s heads up too, and treat the scalding water and fragile ground at undeveloped springs as the more common dangers.