He was known as “charismatic but unpredictable,” the New York Times wrote about Kilmer, who reportedly left Hollywood for a decade to spend more time with his children. 

“I have no regrets,” said Kilmer in a 2021 AP interview. “I’ve witnessed and experienced miracles.”

Kilmer passed away from pneumonia, his daughter reported, according to an email sent to the Associated Press. He had previously recovered from a 2014 throat cancer diagnosis. 

Pneumonia is a serious infection of the lungs that can cause inflammation and a build-up of fluid, making it hard to breathe. The leading cause of pediatric hospitalization and death in children under five, pneumonia is also common in adults. Older adults are at a higher risk for developing pneumonia and dying from it, according to the American Thoracic Society. 

Dr. Carrie Horn, chief medical officer at leading U.S. respiratory hospital National Jewish Health in Denver and a hospitalist, previously told Fortune that bacteria and viruses most commonly cause the infection. 

Pneumonia symptoms

Symptoms of pneumonia include a cough, a fever, shortness of breath, sharp or stabbing chest pain, nausea, and a low appetite, according to the American Lung Association. More severe symptoms include heavy breathing problems, low oxygen levels, long-lasting fevers, and low blood pressure.

Older adults, in particular, may experience confusion and weakness and a lower temperature instead of a fever. These symptoms can mirror myriad illnesses, so it’s essential to monitor them and check with a doctor. 

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“When older people develop pneumonia, they often don’t have the typical symptoms such as a fever or a cough with phlegm,” according to the National Institutes of Health. “This can sometimes make it very difficult to diagnose pneumonia. Older people often need more intensive treatment than younger people, and they have a higher risk of complications.”

Pneumonia can be deadly, killing over 50,000 people in the U.S. annually. Complications include respiratory failure, sepsis, and lung abscess, according to the American Lung Association. In severe cases, it can also affect other organs.

“Someone who becomes very ill with pneumonia may have fluid shifts and also have issues with their kidneys or with their liver or with their heart,” Dr. Clayton Cowl, a pulmonologist with the Mayo Clinic in Rochester, Minn., previously told Fortune. “It can cause a whole kind of downstream effect, a bucket brigade.” 

Pneumonia in older adults is usually treated in a hospital with antibiotics, and, in more serious cases, with IVs and ventilation. Older adults can reduce their risk through good hygiene and by eliminating smoking. For older adults, who are at an increased risk of pneumonia complications, two vaccines are recommended, including the standard flu vaccine and the pneumococcal vaccine.