<p>Fog computing has become an essential model to extend cloud computing capabilities to the network edge, supporting low-latency processing vital for Internet of Things (IoT) applications. The inherently distributed nature of fog computing introduces significant privacy challenges requiring innovative solutions. This systematic review distinctively integrates four thematic areas—privacy-preserving data aggregation, blockchain-based solutions, privacy-preserving authentication/access control, and comprehensive privacy-preserving frameworks—to establish a holistic cross-domain analysis. Unlike previous domain-specific surveys, this integrated perspective explicitly identifies critical cross-cutting insights, such as the necessity of balancing computational efficiency with robust privacy guarantees and the convergence towards lightweight cryptographic approaches suitable for resource-constrained fog environments. Notably, the synthesis reveals that standardized benchmarks remain largely absent across domains, highlighting an overarching limitation and underscoring a fundamental research priority. By unifying traditionally isolated areas, the review uniquely contributes a broader understanding of common challenges and interconnected opportunities, facilitating targeted future research directions and practical decision-making in privacy-preserving fog computing networks.</p>