Swollen Abdomen – Causes, Reasons and Diseases

With the growing global obesity epidemic, a large abdomen is not an uncommon sight. However, this may not always be due to fat. The abdomen can at times become swollen which is a temporary increase in the abdominal circumference. Without a bony and rigid wall like the chest cavity, any disturbances within the abdomen may quickly appear as a swollen abdomen.

What is a swollen abdomen?

A swollen abdomen usually infers fluid accumulation within the abdomen. This is known as ascites. Inflammation is another cause of swelling. However, changes in abdominal circumference may not only be due to fluid accumulation or inflammation. A swollen abdomen is usually noticed visually when the distension is significant. Deeper lying swelling, even a  severely swollen organ within the abdominal cavity, may not always cause noticeable abdominal swelling.

Why does the abdomen swell?

A visible change in the circumference of the abdomen may occur due to a solid mass or fluid accumulation within the abdominal cavity. It is rare for gas to cause abdominal swelling, contrary to popular belief. Furthermore, an accumulation of intestinal gas (gas within the bowels) is unlikely to cause noticeable distention of the abdomen. However, with a condition known as functional bloating it is believed that gas may play a role.

The abdominal cavity is tightly packed with organs but there is still significant space between organs and structures. For abdominal swelling to be evident, there usually has to be a significant increase in solid matter or fluid within the cavity. The location is equally important. Sometimes one part of the abdomen may be visibly swollen or distended and this usually indicates a problem with organs in that area.

It is also important to note that the tautness of the abdominal muscles can affect the abdominal circumference. A person with firmer abdominal muscles may therefore have a flatter abdomen whereas a person who has lax abdominal muscles presents with a distended abdomen. This is due to the pressure within the abdomen pushing the outwards and leading to distension.

Causes of Swollen Abdomen

Swelling of the abdomen may be due to a host of different causes. It is important to differentiate between localized swelling and generalized swelling. With localized swelling, the distension is limited to one region of the abdomen. However, in most instances a swollen abdomen is generalized meaning that entire abdomen is distended. More causes have also been covered under abdominal distension.


Peritonitis is a condition where the lining around the bowels and other abdominal organs becomes inflamed. This lining known as the peritoneum may become irritated when the contents of an abdominal organ leaks out or if it becomes infected. Normally there is a small volume of peritoneal fluid for lubrication. The fluid that is normally within the peritoneal cavity increases significantly.

Read more about peritonitis.


Fat accumulation can also cause distension of the abdomen. Subcutaneous fat is the fat accumulation under the skin surface. It is this fat accumulation in the abdomen that causes a visible distension which we typically associate with obesity and term as the ‘flabby belly’ or ‘paunch’. Another type of fat accumulation can occur around the organs of the abdomen. This is known as visceral fat but usually cannot be seen as a large abdomen.

Fluid Retention

When there is fluid retention, the excess fluid may accumulate in various cavities of the body like within the abdominal cavity. Usually fluid retention is associated with disturbances in the electrolyte levels in the body and this is often a result of kidney disturbances since the kidneys regulate the fluid levels. It may also occur with nutritional deficiencies, like vitamin B deficiency and protein deficiency, lifestyle factors, trauma and cancer.

Read more about fluid retention.


Various cancers cause a swollen abdomen for different reasons. It usually occurs with tumors that release hormones and then lead to disturbances in fluid and electrolytes within the body. Sometimes a very large intra-abdominal mass can cause visible distension of the abdomen. This is sometimes reported with certain massive cancers of the uterus and other organs. However, it is uncommon.


Pregnancy may seem like an obvious cause of a swollen abdomen. However, some women do not know that they are pregnant until there is a visible distension of the abdomen. Apart from the growing uterus which causes distension, pregnancy hormones may also cause fluid retention in the abdomen. It may also affect the abdominal muscles, causing it to be more lax.

Organ Failure

Failure of certain organs may also lead to a swollen abdomen, usually as a result of fluid retention. This is primarily seen with heart, liver and/or kidney failure. The swelling often starts as leg swelling, eventually involves the abdomen and in severe cases there may be generalized swelling known as anasarca. Sometimes fluid may also enter into other cavities within the body, like the lungs (pulmonary edema).


Abdominal trauma can also result in a swollen abdomen. This can be due to a blow to the abdomen, penetrating injury to the abdomen and may also arise with swelling. The reason for this swelling may be as a result of inflammation, fluid or blood accumulation in the abdomen and laxness of the abdominal muscles. It needs to be immediately investigated as the swollen abdomen may be a sign of internal bleeding (blood loss into the abdominal cavity).

Organ Enlargment

If an abdominal organ is enlarged, then there may be visible swelling of the abdomen. This is uncommon as the organ occupies more space in the abdomen but this rarely causes distension. The organs that are more commonly affect are the liver (hepatomegaly) and the spleen (splenomegaly). Sometimes both organs are enlarged and this is jointly referred to as heptaosplenomegaly.

Functional Bloating

Functional bloating is a condition where there is a sensation of fullness along with distension of the abdomen for no clearly identifiable reason. It is often associated with functional bowel disorders like irritable bowel syndrome. The distension can come and go within hours to days. The possibility of gas accumulation has been proposed but it seem to occur in conjunction with laxity of the abdominal muscles.

Read more about functional abdominal bloating.