This paper argues that human capital depreciation during unemployment generates an externality in job creation: firms ignore how their hiring decisions affect the skill composition of the future unemployment pool, and hence the output produced by new hires. As a consequence. job creation is too low from a social point of view. But the extent to which it is too low varies over the cycle. The reason is that the increase in the expected productivity of a new hire from next period's unemployment pool caused by hiring an additional worker today, depends on the pool's composition, which varies over the cycle.