Milk hypersensitivity affects less than 1 percent of adults and approximately 2 to 5 percent of children. According to the Cleveland Clinic, food intolerance results from the body's inability to break down a component of food, such as protein. The milk proteins casein and whey trigger a digestive system response that produces gastrointestinal symptoms in individuals with milk protein intolerance.
Blood in Stool
Milk protein intolerance can cause inflammation in the large intestine and rectum, resulting in blood-tinged stools. This condition is called proctitis or proctocolitis and predominately occurs in infants, according to Dr. Alan M. Lake, associate professor of pediatrics at Johns Hopkins University School of Medicine. Lake states that this symptom typically manifests between 2 and 8 weeks of age and resolves within three days of eliminating the milk protein exposure. Approximately 95 percent of affected infants will be able to tolerate milk protein consumption by nine months of age, says Lake.
Although the frequency of bowel movements can vary from individual to individual, the Mayo Clinic states that having fewer than three bowel movements per week can indicate constipation, as can the passing of hard and dry stools. Milk protein intolerance has been linked to chronic constipation. Researcher Silvia Daher and colleagues reported in the December 2001 issue of Pediatric Allergy and Immunology that 28 percent of the children studied suffering from chronic constipation experienced normal bowel movements when cow's milk protein was eliminated from their diets.
The regurgitation of gastric contents into the esophagus, known as gastroesophageal reflux, can result from an intolerance to milk protein. Up to 40 percent of infants suffering from gastroesophageal reflux are milk protein intolerant, according to Dr. Harland S. Winter, associate professor of pediatrics at Harvard Medical School. The affected individual may experience a sensation of burning in the chest and throat, coughing, wheezing and difficulty swallowing. Infants may refuse to eat as well.
Milk protein intolerance can trigger an inflammatory response in the small intestine, called enteropathy, which interferes with absorption and causes diarrhea. It most often occurs in infants who have been given cow's milk before the age of 9 months. When the entire gastrointestinal system is affected, the condition is called milk protein-induced enterocolitis.
Vomiting or Spitting Up
Vomiting also occurs with milk protein-induced enteropathy and enterocolitis. It typically starts within two to four hours of milk protein consumption and can lead to severe dehydration. Frequent spit-up in an infant can indicate gastroesophageal reflux brought on by milk protein intolerance.