Swollen foot: what are the reasons?

Most commonly, we observe a similar swelling of both feet that can interfere with daily life. There are quite a number of reasons that can explain this:

• Sedentary Lifestyle : Most commonly, foot oedema is due to a lack of physical activity. When one remains seated or in a static position for extended periods, blood and lymph tend to accumulate in the lower limbs of the body. Conversely, when the leg muscles are active, they contract and relax, acting like a pump that pushes fluids towards the heart, thereby reducing the risk of swelling.

• Obesity : Similarly, obesity can cause or contribute to the swelling of the feet. The veins in the lower limbs, whose role is to transport blood back to the heart, are no longer as efficient due to the additional weight exerted on them from the abdomen.

• Hormonal fluctuations : Hormonal changes during the pregnancy or throughout the menstrual cycle can also be responsible for oedema in the feet. Indeed, oestrogen, a hormone whose synthesis significantly increases during pregnancy and whose quantity varies throughout the menstrual cycle, acts primarily by binding to nuclear receptors ER-α and ER-β. In doing so, it triggers a cascade of reactions involving the intensification of the production of intracellular cyclic adenosine monophosphate (cAMP). This, in turn, plays a role in the regulation of the synthesis of nitric oxide (NO), a vasodilator.

• An Endocrine System Disorder : An overactive or underactive thyroid gland can cause swelling or thickening of the skin around the shins and ankles, often hard and waxy in appearance. As a reminder, this organ located in the neck produces the thyroid hormones thyroxine and triiodothyronine, which play a role in regulating calcium metabolism. Found in the blood, calcium is necessary for the proper functioning of the circulatory system.

• Cushing's Syndrome : This disease, in which the adrenal gland produces an excess of steroid hormones, can be responsible for swelling in both feet. Besides this swelling, patients with Cushing's Syndrome typically exhibit other characteristics of the condition, such as changes in skin texture, a roundness of the face, and the appearance of a hump of tissue at the back of the neck.

• Heart Failure : When the heart is weakened, it fails to pump enough blood. This causes the blood to backflow into the veins, leading to an increase in pressure that pushes fluid into the tissues. The blood then tends to pool in the lower limbs, particularly in the feet, resulting in oedema. In addition to swelling, patients suffering from heart failure typically experience rapid shortness of breath during exertion.

• The intake of certain medications : Medications are another common cause of swelling in the feet and legs. This discomfort can particularly be observed with calcium inhibitors, such as amlodipine or nifedipine, non-steroidal anti-inflammatory drugs (NSAIDs), like ibuprofen or naproxen, gabapentin, oral contraceptives, prednisone or with medications fighting against diabetes of the thiazolidinediones type.

• Heat : It is more common to observe swelling of the feet during the summer period. Indeed, when it is hot, the blood vessels dilate to help dissipate body heat, which increases blood flow to the extremities and results in an accumulation of blood and fluids in the feet and ankles. This vasodilation, although necessary for the regulation of body temperature, directly contributes to the swelling of the feet. Moreover, high temperatures increase the permeability of the capillaries, allowing more fluids to escape from the blood vessels into the surrounding tissues.

• The wearing of narrow shoes : By exerting constant pressure on the feet, narrow shoes can cause local inflammation, resulting in swelling of this part of the body. Moreover, ill-fitting shoes can compress the feet and toes, thereby limiting the blood flow to and from the feet. This compression of the blood vessels hinders normal circulation, which can lead to an accumulation of blood and fluids in the feet, exacerbating the swelling.

Less commonly, swelling may affect only one of the two feet. The causes of this peculiarity are then different:

• Venous Thrombosis : The presence of a blood clot in the veins of the ankle leads to swelling of the foot. This swelling appears rapidly, within a few hours to a few days, and causes the patient severe pain and intense redness. Venous thrombosis is caused by a combination of factors: stagnation of blood flow, damage to the veins, genetic predispositions... It is most often observed in patients who have undergone major surgery or significant foot trauma. Urgent medical attention is necessary as soon as a blood clot is suspected.

• Infectious cellulitis : Not to be confused with adipose, aqueous, and fibrous cellulitis, infectious cellulitis is an acute bacterial infection of the skin and subcutaneous tissues caused by streptococci or staphylococci. It is recognised by the erythema, oedema, and pain it causes. Infectious cellulitis is more commonly found in individuals suffering from diabetes or other chronic diseases, but it can also occur in healthy individuals if a cut or scrape allows bacteria to penetrate the tissues. It is treated with antibiotics.

• An Ankle Sprain : More benign, an ankle sprain can also cause swelling of the foot. From a biological perspective, the sprain is due to trauma to the ligaments supporting a joint. It is caused by a sudden and violent movement, accompanied by a twist. Resting the foot for a few weeks is usually enough to fully heal the sprain.

Depending on the circumstances, certain factors may cause swelling in one or both feet:

• Venous hypertension : This issue arises when the veins widen and the valves that prevent blood reflux can no longer close properly. The blood can then no longer return to the heart and stagnates in the legs and feet. The excess blood causes high pressure in the veins, which in turn causes fluid to leak into the tissues. Patients suffering from venous hypertension frequently develop varicose veins, that is, bulging and twisted veins appearing blue-purple. To control the swelling, wearing compression stockings may be sufficient, although outpatient care is sometimes necessary.

• Lymphoedema : Another vascular cause of foot swelling, lymphoedema results from a deterioration of the lymphatic vessels. These vessels normally aim to absorb excess fluid trapped in the tissues. They are also involved in the body's functions to fight against infections. As soon as the first signs of lymphoedema appear, it is necessary to implement a treatment to prevent it from becoming chronic. The most common treatments are lymphatic drainage and the wearing of compression socks.

When the cause is benign, fortunately there are several tricks that can help to reduce swelling in the feet.

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• YANAGISAWA N. & al. Treatment of Leg and Foot Swelling in Women. Women's Health Open Journal (2017).