In colorectal resections, rectal stump lavage is commonly performed prior to primary anastomosis for reducing bacterial counts and minimizing the risk of anastomotic recurrence. Being a potent bactericidal and cytotoxic disinfectant, chlorhexidine is frequently chosen as the irrigation solution of choice for such purposes. Despite its widespread use, the potential for developing chlorhexidine allergy is still a major concern due to the ever-rising number of literature reports of hypersensitivity reactions to chlorhexidine in surgical patients. This report illustrates the first reported case of life-threatening chlorhexidine anaphylaxis after its use in rectal stump lavage for colorectal resection. This report serves as a reminder of the potential danger of this "hidden allergen" in clinical practice.