What causes a change in the demand curve or a shift

Shift along the demand curve is price dependent, assuming other factors that change demand is held constant. Something other than price, such as income, population, consumer expectations, and consumer tastes will shift curve left or right. For example, many a rising population around an area will increase demand for regular household products. This case is not affected by price.

A change in demand will cause a shift to the right for increase and left for decrease.