Why did World War 1 soldiers fear mustard gas?

The soldiers feared it so much because if you got caught in it without your gas mask or if your skin was exposed, it burned your skin. It was even worse if you inhaled it because it burned your lungs and your insides. It was a terrible way to die. This fear was the reason that Adolf Hitler did not use gas in World War Two because he was caught in a mustard gas attack. He survived but was horrified by the suffering around him because of the weapon.