When the Consumer Price Index rose 4.2% year over year in May, it was easy to blame the oil market: the Iran conflict had rattled energy prices, and analysts were quick to call the shock temporary. But beneath the headline number, two components of inflation are flashing harder-to-dismiss warnings — and they have helped push nine of 18 Federal Reserve officials to pencil in a rate hike before year-end.

What core inflation tells you

Economists strip out food and energy to get core inflation — a gauge of underlying price pressure unrelated to commodity swings. Oil prices bounce around for geopolitical reasons; core inflation tells you whether increases are becoming structural. In May, core CPI rose 2.9%, and core PCE — the Fed's preferred gauge — reached 3.3% in April. The Fed at its June 17 meeting raised its 2026 core forecast to 3.3%, up sharply from 2.7% in March.

Trigger one: shelter

Shelter is the single largest part of the CPI basket, more than a third of the index. It is tracked through "owners' equivalent rent" (OER) — essentially what homeowners would pay to rent their own homes. OER is sticky: unlike gasoline, it does not reverse when a crisis eases, because it reflects leases signed months ago, building bottlenecks and a shortage of affordable supply — none of which a quarter-point move fixes quickly. Bank of America argues the housing-driven disinflation that helped suppress prices through 2024 and early 2025 has largely run its course, removing a key source of cooling.

Trigger two: services

Services make up roughly two-thirds of the economy, and their prices are driven less by oil and supply chains than by wages, rents and healthcare — costs that move slowly and tend to stay elevated once they rise. Services prices excluding energy climbed about 3.3% year over year. The worry, voiced by several Fed officials, is that services inflation has become self-sustaining: prices need no fresh oil shock to stay above target if wages and rents keep grinding higher.

Sticky vs. transitory — the Fed's real test

Transitory inflation comes from one-off shocks — a port closure, a war-driven oil spike — and fades as the disruption passes. Sticky inflation lives in housing and services, moves slowly, and yields only to sustained tightening. The Fed misjudged the first for the second in 2021–22. With Warsh — regarded as among the most hawkish chairs in a generation — now in charge, officials appear determined not to repeat it: the June statement dropped its easing bias even as the Fed held rates at 3.50%–3.75%.

Market implications

The dollar is already responding, sitting at a 13-month high as the odds of U.S. rate hikes rise while other central banks cut — the strong-dollar, risk-off backdrop Boursel has tracked through the bitcoin and "debasement trade" selloff. Bank of America projects three quarter-point hikes in 2026, which would carry the funds rate to 4.25%–4.50%.

For investors the distinction matters: an energy-driven spike would be temporary and bond-friendly once it passes, while entrenched shelter and services inflation would require the kind of prolonged tightening that reprices equities and extends the dollar's run. These are scenarios, not forecasts, and nothing here is investment advice.