Contagion risk is the risk that financial distress spreads from one institution, market or portfolio to others through a transmission channel. A firm can suffer because a borrower fails, a funding provider withdraws, or another investor's forced sales depress the assets it holds. Measuring each position's ordinary market exposure can therefore miss losses created by other participants' distress and responses.
The term has several uses. Here it describes shock transmission, including contractual and market-mediated channels. Some empirical research uses a narrower definition: transmission must exceed normal interdependence or what common fundamentals explain. The ECB's discussion of contagion makes this distinction explicit; an empirical claim needs a stated definition and identification method.
Follow the claim from A to B
Consider a wholly synthetic balance-sheet stress, with all amounts in USD millions. Firm B has equity of 15 and an unsecured claim on firm A valued at 20 before A defaults. Stipulate that the claim then has a recovery value of 50% of its previous value, measured on the same valuation date. Hold every other asset and liability of B unchanged; ignore costs and taxes.
| B's balance-sheet item | Before A's default | After stipulated recovery |
|---|---|---|
| Claim on A | 20 | 10 |
| Equity | 15 | 5 |
For an exposure value and a recovery fraction , the scenario loss is
B's equity falls by the same 10, leaving 5. The default has transmitted a credit loss through an actual claim. It has not made B balance-sheet insolvent in this scenario. Positive equity also does not establish that B can meet every payment on time: that requires a separate funding-liquidity assessment. Neither the default nor the recovery assumption is a probability estimate or forecast.
Original synthetic mechanism comparison. The upper arrow follows a contractual loss; the lower arrows show simultaneous exposure to an external shock. All numerical amounts are USD millions.
The connection need not be a loan
Direct claims are only one route. A distressed institution may sell assets to obtain cash. If its sales push prices down, other holders incur valuation losses even when they have no claim on the seller. Those holders may then face collateral demands or sell assets themselves. Overlapping portfolios create the connection; the price response transmits and can amplify the shock. Contagion Accounting separates losses through direct exposures from those generated by fire-sale dynamics and stresses how much the results depend on the assumed price impact.
Information can also transmit distress. News of one failure may cause lenders to reassess similar firms and withdraw funding. That reassessment can reflect rational learning about previously hidden exposures; calling it contagion does not establish that investors are irrational. McNeil, Frey and Embrechts distinguish direct economic links from information-based default contagion in their treatment of portfolio credit models.
The owned lesson Why Manage Financial Risk? Shareholder, Societal, and Quantitative Views, particularly “Endogenous risk,” develops the fire-sale externality: an action that reduces one firm's exposure can increase losses for others. The public page is a preview; the full lesson requires membership.
Shared losses are not sufficient evidence
Suppose two firms independently hold assets exposed to the same interest-rate increase. Both can lose without either firm's distress changing the other's position. That is a common shock. If one firm's subsequent liquidation pushes prices down further and hurts the other, an additional transmission channel appears.
A rise in correlation during a crisis does not, by itself, identify that channel. A useful stress analysis states the initial shock, maps claims and funding links, separates initial valuation losses from losses generated by reactions, and varies uncertain assumptions such as recoveries and sale-price impact. Counting the initial markdown again as a spillover would overstate amplification.
Systemic risk asks a broader question: could impairment of the financial system disrupt financial services with serious consequences for the real economy? Contagion can help produce that outcome, but the loss passed from A to B above does not establish it. Conversely, severe common exposures can create systemwide distress without a failure first spreading from one institution. The BIS discussion of systemic risk covers both interconnections and common exposures.
Sources
- Vítor Constâncio, ECB, “Contagion and the European debt crisis”, 10 October 2011, “The phenomenon of contagion: from research to policy,” on definitions, common shocks and identification.
- Iñaki Aldasoro, Anne-Caroline Hüser and Christoffer Kok, Contagion Accounting, BIS Working Paper 908, 11 December 2020, research overview and abstract on direct and fire-sale channels. The numerical example here is original and does not reproduce that paper's calibration.
- Jaime Caruana, BIS, “Systemic risk: how to deal with it?”, 12 February 2010, introduction and “Concepts of systemic risk.”
- Alexander J. McNeil, Rüdiger Frey and Paul Embrechts, Quantitative Risk Management: Concepts, Techniques and Tools, revised edition, Princeton University Press, 2015, §1.3.3, p. 28, on endogenous risk; §17.1.2, p. 601, on economic links and information-based default contagion.