There is increasing concern that we may be experiencing another round of asset-price bubbles that could pose great danger to the economy. Does this danger provide a case for the US Federal Reserve to exit from its zero-interest-rate policy sooner rather than later, as many commentators have suggested? The answer is no.

Are potential asset-price bubbles always dangerous? Asset-price bubbles can be separated into two categories. The first and dangerous category is one I call “a credit boom bubble”, in which exuberant expectations about economic prospects or structural changes in financial markets lead to a credit boom. The resulting increased demand for some assets raises their price and, in turn, encourages further lending against these assets, increasing demand, and hence their prices, even more, creating a positive feedback loop. This feedback loop involves increasing leverage, further easing of credit standards, then even higher leverage, and the cycle continues.

Eventually, the bubble bursts and asset prices collapse, leading to a reversal of the feedback loop. Loans go sour, the deleveraging begins, demand for the assets declines further and prices drop even more. The resulting loan losses and declines in asset prices erode the balance sheets at financial institutions, further diminishing credit and investment across a broad range of assets. The resulting deleveraging depresses business and household spending, which weakens economic activity and increases macroeconomic risk in credit markets. Indeed, this is what the recent crisis has been all about.