The endless and quick development of data has brought the consideration of analysts to utilize it within the most conspicuous way for decision-making in different rising applications. These huge data are greatly valuable and profitable for logical investigation, increment efficiency in trade, and make strides for humanity. It makes a difference from the open division to commerce exercises, healthcare to way better route, smart cities to national security. Despite the fact that there are more opportunities to work, the obstacles of handling these data have also grown. In this study, various aspects of big data, as well as their applications and limitations, are discussed. This paper focuses on privacy challenges, privacy violations, and privacypreserving techniques in big data, smart cities, and IoT. This paper introduces a comparative study among the different privacy-preserving techniques showing their advantages and their drawbacks to propose a powerful and applicable privacy protection technique that securely guarantees data integrity when dealing with big datasets and sensitive information in important fields.