Milk allergy does not usually lead to constipation, but on the contrary, milk allergy can lead to diarrhea. Many people are intolerant to milk because of the lack of lactase, which is often referred to as diarrhea and even abdominal pain after using milk or other dairy foods. Therefore, milk allergy usually does not cause constipation, but rather causes diarrhea, an increase in the number of stools, and even watery diarrhea or paste-like diarrhea in some patients, which can be improved when milk intake is stopped. If you repeatedly have diarrhea caused by taking milk or dairy products, you may be intolerant to milk or lactase deficiency, so you should reduce or avoid the intake of milk and other dairy products to reduce the impact of milk on the human body.