in Reactions, you may select when you want the reaction to happen, during a user’s journey through a cohort.

• On Entry - triggers the reaction only when the user lands on a page and enters the cohort criteria
• On Exit - triggers the reaction only when the user lands on a page and leaves the cohort criteria
• Every Time - triggers the reaction every time the user lands on a page and meets the cohort criteria

More information on triggering logic can be found here.