The most common cause of incisional hernia is surgical wound weakness. After surgery, the integrity of the abdominal wall is compromised at the incision site, making it a mechanical weak point. Factors such as inadequate wound closure, infection, or poor tissue healing can further weaken the surgical site, leading to herniation of abdominal contents through the defect. While obesity, chronic cough, and constipation increase intra-abdominal pressure and contribute to hernia formation, they do so secondary to the primary issue of impaired wound strength at the incision. Proper surgical technique and postoperative care are critical to minimizing this risk.

Reference: Schwartz's Principles of Surgery, Brunicardi et al., 11th Edition.