Does chametz on Pesach prohibit a mixture in any amount (b'mashehu), or only at the standard 1:60 ratio like other prohibitions?

Synopsis

The Mechaber rules that chametz on Pesach prohibits a mixture in any amount (mashehu), unlike other prohibitions which require 1:60. The Mishnah Berurah explains this is a rabbinic stringency because chametz carries karet and people are not accustomed to separating from it year-round. Some say it is because chametz is a davar she-yesh lo matirin (permitted after Pesach).

Early Acharonim
Late Acharonim
Lenient
Strict
Lesser cited
Major authority

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