Wireless sensor network (WSN) technology has the potential to change the way we live, work, protect and do business, with applications in entertainment, travel, industry, telemedicine, disaster and emergency management. Data aggregation is key technique for power-efficient information acquisition in WSNs. However, data privacy during data aggregation is an important issue when the WSN is deployed in sensitive data applications, such as telemedicine. If the issues associated with data privacy are not seriously considered, the technology would not be trustingly used for many valuable applications. The existing privacy preserving data aggregation protocols provide a method to sustain privacy of collected sensor’s data from external and internal adversaries during data aggregation in WSNs. The basic aim of the paper is to investigate the critical aspects of the existing privacy preserving data aggregation protocols for WSNs and highlight their major limitations. We claim that in future such limitations can be corrected. Our ongoing work is to propose an alternative solution to overcome such limitations, but this will be presented in a future paper.