Causes of Blood Clots in the Foot

Instructor: Adrianne Baron

Adrianne has a master's degree in cancer biology and has taught high school and college biology.

This lesson is going to cover the two types of blood clots. We will take an in-depth look at what causes blood clots to form in the foot and how it happens.

Blood Clots

Barriers to the flow of traffic can be a good thing, but there are also times when traffic barriers are not so good. The same holds true for barriers to the flow of blood in the body. If there is a cut on a blood vessel, then we want a barrier to staunch the flow of blood so that all of our blood doesn't flow out of our bodies. This barrier is a blood clot, a clump of blood cells and proteins, and it acts as a protective measure. It is similar to barriers being put up to prevent you from driving into areas where the road isn't finished or a bridge is out.

In other circumstances a blood clot may form that is not protective or healthy. One that forms and remains where it formed is known as a thrombus. A thrombus can be dangerous if it develops within the blood vessels and is not due to an injury. This is similar to when an accident occurs, blocking traffic on the highway. The blood clumps together and prevents blood from flowing effectively past the blood clot.

The other type of blood clot is an embolus, which is a blood clot that forms in one part of the body and then enters the bloodstream.

An embolus flowing in the bloodstream
Diagram of an embolus

Causes of Blood Clots in the Foot


A thrombus or embolus can occur anywhere in the body. One place where they may occur is in the foot. There are various reasons why a blood clot may occur in the foot. One of the most common causes is immobility, or lack of movement. We aren't just talking about sitting for short periods of time. Rather, we are talking about not moving or walking for extended periods of time, such as after a surgery or injury or due to paralysis.

The muscles in our feet and legs normally help blood to flow through our veins in those areas. This only happens when the muscles are contracting as a result of walking. When we are immobile, the blood flows slower than usual. Slow moving blood will form blood clots.


Atherosclerosis is a condition in which the opening inside blood vessels becomes narrow due to the buildup of plaque and inflammation of blood vessel walls.

Atherosclerosis is a known cause of blood clots in the foot
Diagram showing atherosclerosis

The plaque usually builds up due to a person eating a diet high in cholesterol along with a lack of exercise. This narrowing of the blood vessels creates a smaller opening through which blood can flow, so blood starts flowing slower than it should. We already know from this lesson that slow moving blood will form blood clots.

Excessive Blood Clotting Factors

Another possible reason for blood clots forming in the feet is that there are more than the necessary amount of blood clotting factors present in the blood. As mentioned earlier, we want our blood to clot in order for our blood vessels to stop bleeding. So there should be some amount of blood clotting factors in the blood. But when there are too many blood clotting factors, the blood tends to form blood clots when there isn't a reason to do so. Two instances in which an excess of blood clotting factors commonly occurs are during pregnancy and when taking birth control pills.

Heart Dysfunction

You probably know that the heart is responsible for pumping blood through the body. The heart is designed to pump blood out of the heart, through the body, and back to the heart again. Any dysfunction in the heart's ability to do this creates a scenario for blood clots to form. If the blood is not pumped as hard as it should be, then it will flow slower and blood clots may form. This happens easily in the feet since they are at the farthest point from the heart to which blood needs to flow. Blood may get to the feet and then not have enough force behind it to flow fast enough to prevent blood clot formation in the feet.

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