When a change in price does not affect the quantity demanded of a commodity , the price elasticity of demand is

When a change in price does not affect the quantity demanded of a commodity, the price elasticity of demand is "perfectly inelastic". Perfectly inelastic demand occurs when the quantity demanded of a product remains constant, even if there is a change in price. This means that the price elasticity of demand is zero, indicating that changes in price do not affect the quantity demanded of the product at all. For instance, the demand for life-saving drugs like insulin or heart medications can be considered perfectly inelastic, because their consumption is considered essential, and people are willing to pay any price to get them. Even if the price of insulin doubles, the quantity demanded may still remain the same, as people have no substitute for the drug. Thus, in the case of perfectly inelastic demand, the price elasticity of demand is zero, indicating no change in quantity demanded, regardless of changes in price.