Unsterilized Intervention

An unsterilized intervention is a foreign exchange operation in which a central bank purchases or sells foreign currency, and the resulting change to the monetary base is allowed to flow through to the domestic money supply without offsetting action.

When a central bank intervenes in currency markets, it can take one of two paths. A sterilized intervention neutralizes the effect on domestic money supply by offsetting purchases or sales of foreign currency with opposite domestic asset sales or purchases. An unsterilized intervention skips that step. The monetary effect is felt immediately.

The mechanics: buying foreign currency

Suppose the Brazilian central bank buys dollars to defend the real against depreciation. It issues reais from its account and receives dollars in exchange. Those new reais enter the banking system, adding to the monetary base. Banks receive the reais, lend them out, and the money supply expands. Interest rates fall as credit becomes more abundant. This is unsterilized: the CB made no effort to drain the reais by selling government bonds or raising reserve requirements.

In contrast, a sterilized intervention would pair the dollar purchase with a domestic open-market operation: the CB sells government bonds denominated in reais, draining the reais it just injected. The effect on the FX rate may remain, but the domestic money supply is unchanged.

Why unsterilized is simpler but costly

Unsterilized intervention is cheaper operationally — no secondary transaction needed. It also sends a stronger signal: the CB is not just trying to nudge the currency; it is committing actual monetary fuel to move it. Central banks often use unsterilized intervention in crises, when rapid credit expansion is desired alongside currency support.

The downside is loss of control over the money supply. If the CB wants to buy dollars to strengthen the currency but does not want to loosen monetary policy, sterilized intervention is the right choice. If the CB does want to loosen (or tighten) monetary policy and move the currency, unsterilized intervention kills two birds with one stone.

Contrast with sterilized intervention

A sterilized intervention keeps the monetary base constant, isolating the currency move from the domestic economy. It is the preferred tool of developed-market central banks that are focused on inflation control and stable money supply. Unsterilized intervention is more common in emerging markets, where the CB may be trying to simultaneously adjust the exchange rate and manage credit conditions.

The Fed, ECB, and Bank of England rarely use unsterilized intervention in normal times. They prefer to adjust interest rates (via federal-funds-rate policy) to achieve both monetary and currency goals. Unsterilized intervention happens when interest-rate policy and FX goals are in conflict, or when the CB has exhausted interest-rate room.

Domestic monetary transmission and interest rates

When the CB buys foreign currency unsterilized, it adds base money to the system. Banks hold more reserves, allowing them to expand lending. The money multiplier kicks in: each dollar of new base money spawns several dollars of M2 or M3 (broad money). The yield curve tends to flatten or invert in response, as short-term rates (controlled by the base) fall faster than long-term rates. This creates an expansion-phase dynamic: credit is cheap, borrowing increases, and inflation risk rises.

Emerging-market use cases

Emerging-market central banks often face a dilemma: the currency is under pressure (capital outflows, weak commodity prices), and they want to defend it by buying dollars. But if they sterilize, they must sell local-currency bonds or raise rates, which can trigger more capital outflow. Unsterilized intervention, while it inflates the money supply, signals commitment to the currency and allows banks to continue lending. Brazil, Russia, India, and many other emerging markets have used unsterilized purchases of dollars during crises.

Conversely, when the currency is too strong and the CB wants to weaken it (and allow inflation to rise), unsterilized selling of foreign reserves is a mechanism: it shrinks base money, tightens credit, and allows depreciation to boost exports. Turkey and Argentina have used this approach at times.

Inflation and long-term consequences

The key risk of unsterilized intervention is inflation. By expanding the monetary base without a corresponding increase in goods and services, the CB pushes the economy toward higher inflation. The Phillips curve trade-off suggests that lower unemployment and stronger growth come with higher inflation. Unsterilized intervention makes that trade-off explicit: faster growth and currency stability, but at the cost of rising prices.

Over time, if the CB continues to loosen via unsterilized FX purchases, the real exchange rate may adjust through inflation rather than nominal currency appreciation. Workers demand higher wages because prices are rising, and competitiveness on global markets erodes. This is why developed-market CBs avoid chronic unsterilized intervention.

Credibility and policy signaling

Unsterilized intervention sends a strong signal about the CB’s priorities. If the CB is willing to sacrifice inflation control to defend the currency, it suggests the fixed exchange rate (or target band) is credible. This can stabilize expectations in a crisis. But if the market perceives the unsterilized loosening as excessive or inflationary, it can backfire: the currency depreciates faster as investors flee inflation expectations, and the CB’s effort to support it becomes futile.

The most famous example is Mexico 1994–95: the central bank (Banco de México) defended the peso via reserve sales and interest rate hikes, a form of unsterilized tightening, until reserves ran out. The peso collapsed, and the ensuing inflation spike was severe. The lesson: unsterilized intervention can work in the short term but cannot override fundamental imbalances forever.