3 Endogenous risk factors -Extremes of age : order adults and neonates. -Immunosuppression. -Alcoholism. -Pre-existing infection at another site. -Diabetes mellitus. -Hypothermia. -Poor nutrition or physical status. -Obesity. -Shock. -Length of pre-operative stay. -Previous radiotherapy or chemotherapy. -Skin disease in the area of the wound,for example psoriasis. -Smoking and use of tobacco products. (Barnard 2003,Johns Hopkins Medicine 2010) Exogenous risk factors -Contaminated or dirty surgical procedure,or poor surgical instrument processing. -Operations that last longer than predicted. -Surgical scrub that is not applied for the recommended time. -Excessive movement of staff in theatre. -Foreign material in the surgical site. -Staff with skin infection. -Type of surgery-some operation carry high risk of infection, for example colorectal surgery-and complexity of the procedure. -Surgical drains. -Surgical technique-laparoscopic procedures carry a lower risk of infection than open techniques. -Transplant or implant operations