What is a food sensitivity?
A food sensitivity is developed due to an adverse delayed response to foods that is usually caused by the immune system. 
 
Why do food sensitivity develop?
Typically it is a sign that the foods being consumed are not being effectively digested and larger particles are entering the bloodstream as undigested proteins which can trigger an immune response. This simply looks to break down the larger undigested food to smaller molecules that can be absorbed. Similarly how the immune system attacks a virus to break down a pathogen. As a result of this it caused inflammation in the body that provoked symptoms. It can be said that food sensitivity can be associated with your favourite foods those that are consumed in high quantities, but there are many other factors to consider:
How food is processed
How intensive animals are rears
Fertilisers used in the farming process
Overconsumption of antibiotics
Genetics
Stress
Poor gut bacteria
Leaky gut syndrome