Protein intolerance (CMPI) (sometimes called allergic proctitis) is a common cause of bloody stools in an otherwise healthy infant. The disease is caused by an abnormal reaction of the immune system to one or more food proteins - the most common being cow’s milk and soy protein. This reaction can cause irritation/inflammation in the distal part of the intestine and can lead to a wide range of clinical symptoms. These proteins are also found in yogurt, cheeses and other dairy products. Cow’s milk proteins can pass into breast milk, and breast-fed babies with CMPI may have symptoms if there is milk in their mother’s diet.
CMPI is different from lactose intolerance or a milk allergy. It’s more likely in babies who have a close relative who had CMPI or has allergies. Most babies outgrow this condition by one year of age, although in some children it may take 2-3 years.