 perovskite solar cells, PSEs, have been hailed as one of the most promising next generation photovoltaic technologies due to their rapid increase in power conversion efficiency. However, the instability of perovskite layers has been identified as a major obstacle to their widespread adoption. This review paper examines the chemical reactions of perovskite layers under different environmental conditions, including moisture, oxygen, light, and with charge transfer materials and metal electrodes. Strategies for mitigating these reactions, such as the use of buffer layers and additive engineering, are discussed. Finally, conclusions and future directions for the field are presented. This article was authored by Jing Zhuang, Jijing Wang, and Feng Nian.