Irritable Bowel Syndrome (IBS): This is a common condition characterized by recurring abdominal pain and changes in bowel movements, often presenting with loose stools. The diagnosis is often made based on symptom criteria, as there are no specific tests to confirm IBS.

Infectious Gastroenteritis: Viral or bacterial infections can cause loose stools, and this condition is often self-limiting but can be severe in certain cases.
Lactose Intolerance: The inability to digest lactose, a sugar found in milk and other dairy products, can lead to loose stools after consuming these products.
Gastroesophageal Reflux Disease (GERD): Although primarily known for causing heartburn, GERD can also lead to loose stools in some individuals.
Inflammatory Bowel Disease (IBD): Conditions like Crohn's disease and ulcerative colitis can cause chronic inflammation of the gastrointestinal tract, leading to symptoms including loose stools.

Celiac Disease: An autoimmune disorder where the ingestion of gluten leads to damage in the small intestine, causing malabsorption and potentially life-threatening complications if left untreated.
Giardiasis: An infection caused by the Giardia parasite, which can lead to severe and prolonged diarrhea if not properly treated.
Thyroid Disorders: Both hyperthyroidism and hypothyroidism can affect bowel movements, with hyperthyroidism more commonly associated with loose stools.
Medication Side Effects: Certain medications, such as antibiotics, antacids, and laxatives, can cause loose stools as a side effect.

Whipple's Disease: A rare, systemic bacterial infection that can cause malabsorption and lead to symptoms including loose stools.
Short Bowel Syndrome: A condition where a significant portion of the small intestine is missing or not functioning, leading to malabsorption.
Bile Acid Diarrhea: A condition where the body has too much bile acid in the colon, leading to chronic diarrhea.
Microscopic Colitis: A type of inflammation of the colon that can cause chronic, watery diarrhea.