This set of symptoms typically include a feeling of dread or helplessness that may coincide with panic, fear, flight, or an inability to reason, sleep, walk, or talk.

In World War II and beyond, the diagnosis of "shell shock" was replaced by that of combat stress reaction, which is a similar but not identical response to the trauma of warfare and bombardment.

During the early stages of World War I, in 1914, soldiers from the British Expeditionary Force began to report medical symptoms after combat, including tinnitus, amnesia, headaches, dizziness, tremors, and hypersensitivity to noise.

Some physicians held the view that it was a result of hidden physical damage to the brain, with the shock waves from bursting shells creating a cerebral lesion that caused the symptoms and could potentially prove fatal.

[8] As the size of the British Expeditionary Force increased, and manpower became in shorter supply, the number of shell-shock cases became a growing problem for the military authorities.

[8] Col. James Samuel Yeaman Rogers (1868–1949),[12] Regimental Medical Officer, 4th Battalion Black Watch wrote:You must send your commotional cases down the line.

[7]: 1643 The treatment of chronic shell shock varied widely according to the details of the symptoms, the views of the doctors involved, and other factors including the rank and class of the patient.

[4] In addition to establishing 19 British military hospitals specifically for the treatment of shell shock, the condition's frequent occurrence among troops during World War I sparked intense discussions over its nature.

The severity of the condition, which was initially written off by some as weakness or cowardice, and the fact that it persisted long after the war prompted a reassessment of mental health in military settings.

The long-term effects of psychological trauma on soldiers and the healthcare systems of post-war nations are highlighted by the ongoing care for shell-shock victims, such as the 65,000 British veterans who are still receiving therapy ten years later and the French patients who were seen in hospitals into the 1960s.

This understanding of combat trauma's aftereffects opened the door for more thorough research on psychological harm, which in turn helped to formalize diagnoses like post-traumatic stress disorder (PTSD).

The combined psychological and physiological aspects of shell shock are further highlighted by recent neurological research, such as that conducted by Johns Hopkins University, which links it to quantifiable brain deficits in veterans.

Research by Johns Hopkins University in 2015 found that the brain tissue of combat veterans who had been exposed to improvised explosive devices exhibited a pattern of injury in the areas responsible for decision making, memory, and reasoning.

This evidence has led the researchers to conclude that shell shock may not only be a psychological disorder, since the symptoms exhibited by affected individuals from the First World War are very similar to these injuries.

[14] Additional research from Uniformed Services University of the Health Sciences on the brains of deceased armed forces service members found that "all five cases with chronic blast exposure showed prominent astroglial scarring that involved the subpial glial plate, penetrating cortical blood vessels, gray–white matter junctions, and structures lining the ventricles; all cases of acute blast exposure showed early astroglial scarring in the same brain regions.

[18] A 2024 New York Times investigation found that U.S. Navy SEALs who died by suicide suffered brain damage from years of repeated blast exposure during training and combat.

[10]At the beginning of World War II, the term "shell shock" was banned by the British Army, though the phrase "postconcussional syndrome" was used to describe similar traumatic responses.

[a] Author Pat Barker explored the causes and effects of shell shock in her Regeneration Trilogy, basing many of her characters on real historical figures and drawing on the writings of the First World War poets and the army doctor W. H. R. Rivers.

Although the term "shell shocked" is typically used in discussions of WWI to describe early forms of PTSD, its high-impact explosives–related nature provides modern applications as well.

The study revealed that, while the brain remains intact immediately after low-level blast effects, the chronic inflammation afterwards is what ultimately leads to many cases of shell shock and PTSD.