Which of the following factors is least likely to cause complex cysts?

Complex cysts, particularly in the context of ovarian cysts, can arise due to various factors, but hormonal influence is generally not the primary or most direct cause for their development. Hormonal influences often lead to the formation of functional cysts, such as follicular or corpus luteum cysts, which are usually benign and resolve spontaneously without complications.

In contrast, infection can lead to the formation of complex cysts by causing inflammation and the accumulation of fluid or pus within a cyst. Structural damage, such as trauma or prior surgery, can also result in the development of complex cysts due to scarring or alterations in normal tissue architecture. Neoplastic changes can result in complex cysts as well, particularly in the context of tumors that may produce cystic structures.

Thus, while hormonal fluctuations play a significant role in various types of cyst formation, the process of complex cyst development is less directly associated with hormonal influence, making it the least likely factor among the choices presented.