Within seconds of the collapse of the World Trade Center in the September 11 attacks, building materials, electronic equipment, and furniture were pulverized and spread over the area of the Financial District of Lower Manhattan. In the five months following the attacks, dust from the destroyed buildings continued to fill the air of the World Trade Center site. Many New York residents have reported symptoms of Ground Zero–related respiratory illnesses.

Various health programs have arisen to deal with the ongoing health effects of the September 11 attacks. The World Trade Center Health Program, which provides testing and treatment to 9/11 responders and survivors, consolidated many of these after the James Zadroga 9/11 Health and Compensation Act became law in January 2011.

More people have died from illnesses caused by 9/11 than during the attack itself. As of 2023, it is estimated that over 5,000 people have died from medical complications related to the attacks, specifically those enrolled in the World Trade Center Health Program by the Centers for Disease Control and Prevention.

Exposures and conditions

As of December 2017, the most common conditions certified by the World Trade Center Health Program were rhinosinusitis, gastroesophageal reflux disease (GERD), asthma, sleep apnea, cancer, post-traumatic stress disorder, respiratory disease, chronic obstructive pulmonary disease, depression, and anxiety disorder. The most common cancers were skin cancer and prostate cancer. The World Trade Center Health Program regularly publishes the most commonly certified condition on its website.

Toxic dust

The dust from the collapsed towers was "wildly toxic", according to air pollution expert and University of California, Davis Professor Emeritus Thomas Cahill. Much of the thousands of tons of debris resulting from the collapse of the Twin Towers was pulverized concrete, which is known to cause silicosis upon inhalation. The remainder consisted of more than 2,500 contaminants, more specifically: 50% non-fibrous material and construction debris; 40% glass and other fibers; 9.2% cellulose; and 0.8% of the extremely toxic carcinogen asbestos, as well as detectable amounts of lead and mercury. There were also unprecedented levels of dioxins and polycyclic aromatic hydrocarbons (PAHs) from the fires which burned for three months.Dr. Dennis Charney, in the September 2006 edition of Environmental Health Perspectives, the journal of the National Institute of Environmental Health Sciences Many of the dispersed substances (asbestos, crystalline silica, lead, cadmium, and polycyclic aromatic hydrocarbons) are carcinogenic; other substances can trigger kidney, heart, liver and nervous system deterioration. This was well known by the EPA at the time of collapse. A case report funded by the National Institute for Occupational Safety and Health (NIOSH) and performed by Mount Sinai School of Medicine observed carbon nanotubes in dust samples and in the lungs of several 9/11 responders.

The composition of the smoke and dust in the air was not fully understood at the time; the World Trade Center Health Program's Dr. Michael Crane touched upon this issue in an interview with Newsweek stating:

These toxic exposures have led to debilitating illnesses among rescue, recovery, and cleanup workers, and the pulmonary fibrosis death of NYPD member Cesar Borja.NOTE: son's name spelled differently -ASSOCIATED PRESS, Bush May Meet With Dead Officer's Son, The New York Times, January 30, 2007Carl Campanile, "Kin Suing City over 'WTC toxin' Death". New York Post, January 29, 2007, p. 2Jeff Stier, "The Mystery of Lung Disease", New York Sun, February 20, 2007 Increasing numbers of cases are appearing in which first responders are developing serious respiratory ailments. Health effects also extended to some residents, students, and office workers of Lower Manhattan and nearby Chinatown.

Dr. Edwin M. Kilbourne, a high level federal scientist, issued a memo on September 12, 2001, to the Centers for Disease Control and Prevention advising against the speedy return to buildings in the area because of possible hazards from various toxic materials.

On October 6, 2001, Associate City Health Commissioner Kelly McKinney said that proper safety protocol for WTC site workers was not being enforced.

In September 2026, New York City released approximately 170,000 pages of previously undisclosed records concerning air quality, health concerns, and the city's response to the September 11 attacks. The records included the "Harding Memo", which addressed potential litigation related to exposure to hazardous substances at the World Trade Center site and the lack of adequate protective equipment. The release followed a legal battle with 9/11 Health Watch over access to the records.

Environmental measurements documenting asbestos and other contaminants in Lower Manhattan following the attacks. Some records showed contaminant levels exceeding applicable limits while others documented continued asbestos contamination months after the attacks.

A study of 5,000 rescue workers published in April 2010 by Dr. David J. Prezant – the chief medical officer for the Office of Medical Affairs at the New York City Fire Department – found that all the workers studied had impaired lung functions, with an average impairment of 10 percent. The study found that firefighters who arrived on the Sept. 11 morning had the worst impairments, which presented themselves within the first year after the attack, with little or no improvements in the ensuing six years. 30% to 40% of workers were reporting persistent symptoms and 1000 of the group studied were on "permanent respiratory disability". A 2006 study has discovered that first responders were losing 12 years of lung capacity. The World Trade Center Health Program certified such conditions as rhinosinusitis, asthma, GERD, COPD, and cancer. Dr. Prezant noted that medication given to the victims can ease but not cure the symptoms. Dr. Byron Thomashow, medical director of the Center for Chest Disease and Respiratory Failure at New York – Presbyterian/Columbia hospital, said that "The drop-off in lung function initially is really quite significant and doesn't get better. That's not what we've generally come to expect in people with fire and smoke exposure. They usually recover."

Cancer risk

A study published in December 2012 in The Journal of the American Medical Association observed the possible association between exposure to the World Trade Center debris and excess cancer risk. Over 55,000 individuals enrolled in the World Trade Center Health Registry, separated by rescue and/or recovery workers and non-rescue and/or recovery workers, were observed from 2003 or 2004 to December 31, 2008. The findings showed the overall incidence of all cancers among rescue and/or recovery workers was not significantly elevated, compared to non-rescue and/or recovery workers. Despite this, the incidences for prostate cancer, thyroid cancer and multiple myeloma were significantly elevated among the rescue and/or recovery workers in the final year of observation. There were higher rates of cancer in the firefighters exposed to the WTC than in the general population of male individuals in the United States in 2001-2016, with major adjustments observed in melanoma, thyroid cancer and non-Hodgkin lymphoma. The highest number of cancer cases and cancer deaths recorded under the WTC Health Program have reached 8,215 and 143, respectively.

On November 28, 2006, the Village Voice reported that several dozen recovery personnel have developed cancer – as opposed to having contracted respiratory ailments, and that doctors have argued that some of these cancers developed as a result of the exposure to toxins at the Ground Zero site: "To date, 75 recovery workers at ground zero have been diagnosed with blood cell cancers that a half-dozen top doctors and epidemiologists have confirmed as having been likely caused by that exposure."

On September 11, 2018, 17 years after the attacks, a New York City law firm reported that at least 15 men were diagnosed with male breast cancer in the intervening years due to the attacks.

On September 7, 2025, the New York Post reported the number of people diagnosed with cancer increased by 143% in five years to 48,579, including 8,215 deaths, according to the World Trade Center Health Program.

Through the September 11th Victim Compensation Fund (VCF), individuals who had been diagnosed with cancer as a result of their physical exposure to the toxins in the World Trade Center blast zone or the surrounding New York City area between September 11, 2001, and May 30, 2002, were able to receive financial compensation for the collateral damage they personally suffered because of the attack. Through free legal guidance, affected individuals could clarify their specific eligibility for the VCF, while receiving the necessary logistic aid in order to fulfill a compensation claim by the July 29, 2021 cut-off date for "timely" applications.

Psychological effects

A study published two months after 9/11 found that Americans across the country experienced substantial symptoms of stress after the attacks. Two subsequent studies found that exposure to the attacks was a predictor of the development of PTSD. Additional studies also looked at the psychological effects of those who lost a family member or friend in the attacks, or viewed the attacks on television.. Among higher exposure rates of chronic mental illness, PTSD, depression and anxiety were significantly higher ten years following the attacks. Even seven to nine years post-attack, the rescue and recovery personnel were still left with a range of comorbid conditions and had to be provided with a multidisciplinary way of treatment. Measures have been suggested to diagnose the population affected to heal in the long-term as the psychosocial resilience community level is understood.

Reactions Dr. Larry Norton of Memorial Sloan-Kettering Hospital asked, "Why isn't the whole nation mobilizing to take care of the chronic health impact of this disaster?" Dr. Norton cited the 70 percent illness rate among first responders as "a wake up call." Dr. Nathaniel Hupert of Weill Cornell Medical College, quoted by Jill Gardiner of the October 4, 2006, issue of the New York Sun said that premature deaths and other ailments of dogs in the area are "our canary in the coalmine."

A number of professors and researchers have argued that the cancer incidence among monitored individuals cannot be called a coincidence. They include Richard Clapp and David Ozonoff, professors of environmental health at Boston University School of Public Health, Michael Thun, director of epidemiological research at the American Cancer Society, Francine Laden, assistant professor of environmental epidemiology at Harvard School of Public Health, Jonathan Samet, chairman of the epidemiology department at Johns Hopkins Bloomberg School of Public Health, and Charles Hesdorffer, associate professor of oncology at Johns Hopkins School of Medicine. They assert that the Ground Zero cloud was likely the cause of the illnesses. The American College of Preventative Medicine is concerned that malignant mesothelioma will develop among persons exposed to Ground Zero air.BBC News online Friday, April 26, 2002, 16:19 GMT 17:19 UK "Ground Zero cancer fears"

Monitoring and compensation

About 400,000 people that were directly affected by the attack are eligible to be enrolled in the World Trade Center Health Registry, and can be referred to the World Trade Center Health Program, which provides free monitoring and health care to those enrolled.