A continuous authentication system and related methods are provided. The system detects requests to perform user actions. A security value is associated with each user action. The system determines a subsequent session security level in response to an adjustment to a session security level by a security value of a requested user action. The requested user action is permitted and the session security level is adjusted based on the security value of the requested user action in response to a determination by the system that the subsequent session security level is greater than or equal to a threshold session security level. A user authentication challenge is caused (e.g., prompted) in response to a determination by the system that the subsequent session security level is less than the threshold session security level. The requested user action is permitted and the session security level is adjusted based on the security value of the requested user action in response to a successful user authentication challenge. The requested user action is rejected in response to an unsuccessful user authentication challenge.