Some of the causes of disease are
1.environmental factors like diseases caused by malnutrition industrial hazards or climate
2. specific infective agents like worms protozoans fungi bacteria or viruses
3.inhert defects of organism as genetic anomalies
4 . Combination of these factors
human health gets negatively affected due to physiological malfunctioning , psycological reasons or pathogenic organisms
Bad environment
unhygienic food
no proper diet
no proper time for consumption
are some of the main reasons
  for example when we don't consume some sought of food which is kept for more than 1 day and then we finally consume it,and the food which is consumed may be spoiled  and may trouble our stomach which is called food poisining
this may result in motion's and even in fever