Apart from death and injury through direct enemy activity – raids, attacks, shelling, snipers and artillery fire – soldiers suffered from a range of health problems. Many were ultimately fatal or severely debilitating, and must therefore be considered within the question addressed by this investigation.

Men living in the trenches were surrounded by death. Every day they heard machine guns and rifles trying to kill them. In the evening they heard shells whizzing over their head, and worried all night of being buried alive by a collapsing trench. Before an attack there was always an intense artillery bombardment. Being fired at by these massive guns had an inevitable effect, and men were terrified as they sat helpless in their flimsy dugouts, listening to each shell’s flight and explosion.

The stress of sudden death damaged many soldiers, and caused terrible mental problems (Fig.15). The name of this condition was shellshock. Its symptoms were no less horrible than the causes. Sufferers lost control of their bodies and shook terribly, foaming at their mouths; others became incontinent.

Doctors did not recognise the condition at the time, and diagnosed it as "cowardice". The army punished the sick man in its own way, and over three hundred innocent men were put to death many of whom were shellshock victims. Later in the war, the army began to recognise it as a medical condition, and the sufferer was given work away from the front. But even then, shellshock was not normally recognised until the man shook from head to toe. By this late stage, the victim would often suffer lasting psychological effects.

With mud, dirt and decay, conditions in the trenches were clearly unsanitary. The scourge of infantry on both sides was a louse. Lice are parasites that lived in soldier’s clothes, and on their bodies. Because of the unclean conditions, lice very quickly spread . Soldiers spent much of their time delousing their clothes, or "being chatty" as it was known. Although a hot iron applied to the seams of clothes was most effective, most had to just improvise.

The army did try to stop lice by washing clothes and providing chlorine baths. These killed the lice, but not their eggs and they soon returned. As well as being very demoralising to troops, lice could be painful causing a horrible itching round the neck, wrists and ankles, and even deadly diseases like typhus, and the less serious "Trench fever".

Trudging around in water and mud led to the skin going black and starting to decay (Fig.16). For some it became so bad that the foot had to be amputated:

To catch trench foot in its early stages, the officers inspected their men’s feet and made sure oil was rubbed in. Wet socks were meant to be replaced, but in reality these too were soon sodden.

Wherever soldiers went, rats seemed to follow, sensing a free meal. The trenches were no different. As well as being irritating, rats spread diseases which took many lives. Rats fed off dead and dying animals and men, and they soon got fat on this huge supply of food. These so-called "corpse rats" might even start eating sleeping or drowsy troops. One particularly unlucky soldier experienced this: