Weeks after Hurricanes Milton and Helene tore paths of destruction across the Southeast, pictures of communities left in ruins continue to emerge.

We can easily see damage from the threats we commonly connect with hurricanes and tropical storms: winds, waves, and floodwaters.

But the lingering health problems these storms leave in their wake are mostly invisible, damaging well-being and increasing the risk of disease in insidious and silent waves. From immediate risks from disruptions of medical care to a slow worsening of preexisting chronic conditions, these events can have devastating health impacts – and official death tolls only scratch the surface. More than 7,000 deaths can be linked to a given major hurricane up to 15 years after the storm waves have receded, according to new research.

But the good news is that recognizing the full range of health threats can help families, communities, and health care systems prepare and recover long after landfall.

Immediate health risks: direct injury and contamination

When hurricanes strike, the immediate risk of physical injuries often dominates our attention.

Debris mobilized by winds or water can cause anything from minor cuts to serious trauma. Drownings from floodwater can occur, and downed power lines and floodwaters surging into homes can cause electrocution.

Less visibly, floodwater can mix with dangerous contaminants: Industrial chemicals, fossil fuels, and sewage can turn these waters into toxic stew. Contact with contaminated water can lead to skin injuries and infections, particularly in anyone with an open wound. Exposure to floodwater contaminated by human or animal waste can also increase the risk of gastrointestinal illnesses.

Using data from Hurricane Harvey in 2017 in Texas, researchers compared the rate of emergency department visits in places with low, medium, and high impact from the hurricane based on the amount of flooding. They found that on the day of the hurricane, emergency department visits decreased. This is not surprising as many people may be unable to leave their homes during hurricane conditions and many others may have evacuated from their communities.

But during the immediate aftermath, they saw higher rates of visits for carbon monoxide poisoning in high flood areas, possibly linked to faulty or damaged equipment from flooding or exposure from running generators. They also found higher rates of drownings and hypothermia.

Short-term health impact: Hospitalization and health system risks

In the days and weeks after a hurricane has passed, the health impacts often shift.

Stagnant water left behind can become a breeding ground for mosquitoes, which can carry dengue, West Nile virus, and other mosquito-borne illnesses. Flooded homes also lead to bursts of mold, which can cause respiratory problems.

Other types of infections can also spike. Data from the Florida Department of Health shows an uptick in Vibrio vulnificus infections after the recent hurricanes. Commonly known as flesh-eating bacteria, these microbes are normally found in warm salt water and can be especially dangerous for people with cuts or wounds. More people can come into close contact with this bacteria when hurricanes force seawater into freshwater canals and rivers.

One study using Medicare data from 1999 through 2014 identified several trends for hospitalization in patients over the age of 65. After the first day of the hurricane, hospitalizations increased for a wide range of conditions over a seven-day period: skin diseases, respiratory diseases, injuries, infectious diseases, and even some nervous system diseases. On the other hand, the data showed that hospitalizations for cancers decreased. Though it is not exactly clear why this would be the case, it may be because preplanned treatments were delayed due to damage to hospital infrastructure or problems with communicating about appointments after major flooding.

Another study of 19 million preterm births from 1989 to 2002 across the eastern United States found that pregnant people who experienced a hurricane showed an increased risk of preterm birth. The risk was especially high in already marginalized communities.

Hurricanes can also harm health by disrupting critical health care infrastructure. Severe storms often damage the hospitals and health systems in their path, cutting off power, eliminating access to clean water, contaminating equipment and medications, and forcing evacuations. Even when facilities remain open, damaged roads may prevent safe access to care.

After Hurricane Helene, the U.S. Department of Health and Human Services declared public health emergencies throughout the Southeast. The department deployed over 400 personnel to boost health care services and ensure the safety of hospitals, nursing homes, dialysis centers, and other infrastructure after severe flooding in many parts of the region potentially contaminated and damaged these facilities.

On top of the damage to health infrastructure, storms can disrupt health care supply chains, leading to health impacts far removed from the site of damage. This has been a major concern after Hurricane Helene severely damaged a facility in North Carolina that is a major supplier of IV fluids for the U.S. medical system, worsening a shortage of IV fluids across the country. This shortage is delaying surgical procedures, dialysis, and other types of health care throughout the country, even in places far removed from those directly affected by the hurricane.

Long-term health effects: Chronic disease and mental health conditions

Long after the floodwaters have receded, chronic disease and mental health impacts can linger.

A recent study by economists and public policy experts estimates that death tolls in the days to weeks after a storm provide only a small glimpse of the number of early deaths that occur long after recovery is underway. When the researchers looked at death data from the population left behind, they found trickles of early deaths year after year – long after visible signs of hurricane damage may have disappeared. These are known as indirect deaths – deaths from worsened chronic disease, such as those that may have been avoided if access to electricity-dependent medical equipment like oxygen for patients with emphysema or refrigerated insulin for patients with diabetes had not been disrupted. These effects can linger for up to 15 years after the storm.

To reach that conclusion, the researchers analyzed data from 501 storms between 1930 and 2015 that hit the United States. The analysis found that official death counts in the weeks to months after an event massively underestimates the indirect deaths among hurricane survivors. Their models suggest that more than 7,000-11,000 deaths every year can be linked to each storm – a number 300 times greater than official death counts.

The researchers speculated that the “extra” deaths they found may result from worsened chronic disease management after a life-altering event, which could worsen heart conditions or lead to chronic mental health challenges. They also point to social and economic factors that have major downstream effects on health. For example, regions that must invest in rebuilding devastated infrastructure may invest less in health-supporting programs for decades after a major storm.

Evidence from survey of Hurricane Maria survivors in Puerto Rico in 2017 aligns with the findings. Hurricane Maria was a Category 5 storm and caused substantial devastation on the island. The official death count was 64, but subsequent studies, including one that collected a large amount of survey data from survivors, suggested that over 4,600 extra deaths had occurred in the aftermath of the storm – more than 70 times the official estimate.

Researchers found that many people spent substantial time without water and electricity, and many were unable to access basic medical services like prescription refills. Conditions were worse for people who lived in more remote areas compared to those in city centers.

Compounding the risks to physical health are the invisible scars of mental health conditions. More than a decade after Hurricane Katrina devastated New Orleans, one out of six survivors still showed symptoms consistent with post-traumatic stress disorder, or PTSD. But even diagnoses such as PTSD miss the broader range of mental health struggles and emotional stress that may not meet the criteria for a specific diagnosis but may affect people in their daily lives.

Preparing for the future: Building resilience

As climate change-fueled hurricanes grow stronger and more intense, impacts on health and health care systems will continue to emerge.

The trauma from the experience of a devastating hurricane can have ripple effects for decades. For patients, living without important medications or interventions can lead to a downward health trajectory that is difficult to recover from.

Letting your doctor know about a major storm exposure may help. For example, health providers already recognize that housing status, early childhood trauma, and access to transportation all have long-term impacts on health. Health systems may need to start addressing climate disaster exposure and provide additional support services to combat the major long-term health problems that can come years after these destabilizing events.

Harnessing data about these impacts – near and long term – understanding which communities are at greater risk, and investing in strong health system infrastructure are critical for preparing and minimizing the broad range of health risks.