The case of Kerry Mackin shows why the U.S. has demanded that carmakers recall cars with Takata Corp. air bags nationwide, even at the potential risk of endangering drivers who most urgently need replacements.

Alarmed by reports of fatal air bag explosions, Mackin recently brought her 23-year-old daughter's 2003 Toyota Corolla to a nearby dealership, only to find it was ineligible for repairs. Massachusetts was not among the high-humidity areas covered by recalls of nearly 8 million cars the last two years.

"It doesn't make sense," said Mackin, 66, who lives north of Boston. "Anybody driving one of these cars is experiencing anxiety that the air bag might explode."