Usually, it is easy to pinpoint the cause of a bruise. Often, the culprit is an acute injury. Sometimes, however, bruising seems to occur for no apparent reason. If unexplained bruising appears a lot on the legs, it could be a symptom of an underlying health condition.

Bruising often occurs when blood vessels beneath the skin incur damage. Blood leaks out of the vessels and pools beneath the skin, which causes skin discoloration.

This article will look at the potential causes of unexplained bruising on the legs. It will also cover when to see a doctor.

Some people bruise more easily than others. The following sections will look at some of the factors that may increase a person’s likelihood of bruising.

Age

As a person ages, they become more susceptible to bruising. Bruises may also take longer to heal in older adults.

Family history

According to one older study, people with close family members who bruise easily may also experience frequent bruising.

The Centers for Disease Control and Prevention (CDC) also note that some inherited bleeding disorders, such as von Willebrand’s disease, can make people more susceptible to bruising.

Most of the time, bruising occurs when a person bumps into things, falls, or injures themselves in another way. Bruises typically heal within a few weeks and are usually benign.

Sometimes, however, bruising is a symptom of a more significant health issue.

The following are a few of the possible conditions that may cause random bruising to appear on the legs.

Vitamin deficiencies

People who experience malnutrition could be deficient in vitamin C and may develop scurvy. Other people at risk of developing scurvy include older adults and people who drink a lot of alcohol.

Symptoms of scurvy include bleeding issues that may lead to bruising.

People deficient in vitamin K may also bruise more often. This is because their blood does not clot efficiently.

Although anyone can experience a vitamin K deficiency, it is more common in infants, as breast milk does not contain much of this nutrient.

Liver disease

A damaged liver affects the body’s ability to form clots and stop bleeding. According to the American Liver Foundation, people with cirrhosis may bleed or bruise more easily.

Other symptoms of cirrhosis include:

  • swelling of the legs and abdomen
  • yellowing of the skin, or jaundice
  • severe itching

Treatment

If a person receives a diagnosis of liver disease early enough, the odds of the liver healing itself are higher.

The treatment pathways for liver disease — and cirrhosis, in particular — aim to prevent further liver damage and protect the remaining healthy tissue.

Because alcohol abuse disorder is a common cause of liver disease, some treatments may involve alcohol rehabilitation to help the person stop drinking and prevent further liver damage.

Autoimmune conditions

Some autoimmune conditions, such as rheumatoid arthritis and lupus, may cause unexplained bruising.

Certain medications that help treat rheumatoid arthritis, including corticosteroids, may also contribute to random bruising.

Thrombocytopenia

Thrombocytopenia is a condition that involves low blood platelet counts. When there are not enough platelets, the blood does not clot properly, which could increase the risk of a serious bleed.

Complications from the following may give rise to thrombocytopenia:

Approximately 5–10% of pregnant people and those who have recently given birth develop gestational thrombocytopenia.

Some cancer treatments, such as chemotherapy, could increase a person’s risk of bleeding and bruising. This is because these therapies reduce the amount of platelets in the blood.

Some other symptoms of a low platelet count include:

In severe cases, thrombocytopenia may cause internal bleeding and brain hemorrhage.

Treatment

There are several treatment options for thrombocytopenia. These include:

  • corticosteroids
  • immunoglobulins
  • blood or platelet transfusions
  • splenectomy

Rare clotting issues and bleeding disorders

People with certain bleeding disorders may experience more frequent bruising. Some of these disorders include:

  • Factor V deficiency: This rare genetic bleeding disorder causes frequent nosebleeds, bleeding, and bruising. It affects approximately 1 in 1 million individuals and is more common in India and Iran.
  • Bernard-Soulier syndrome: People with this disorder bruise more frequently, have a higher risk of nosebleeds, and may experience random bleeding.
  • Hemophilia: More males than females have hemophilia. People with this condition are missing factor VIII or IX. These factors are essential proteins involved in the blood clotting process.

Other symptoms that people with blood disorders may experience include:

  • nosebleeds
  • bleeding gums
  • blood in the stool or urine
  • cuts that bleed for a long time
  • heavy periods

Treatment

Treatment options for bleeding disorders vary but may involve platelet transfusions, clotting factors, or medications to help with clotting.

Cancers

Several cancers that affect the blood cells can also cause random bruising. One of these cancers is multiple myeloma. The symptoms of this condition include thrombocytopenia, which lowers blood platelet counts and leads to bleeding and bruising.

Also, some of the initial symptoms of leukemia include bruising and bleeding, with bruises typically appearing on the back, legs, and hands.

Cancer is often treatable, especially when a person receives an early diagnosis. Treatment options vary depending on cancer type, but they may include medication, chemotherapy, and surgery.

Sepsis

Sepsis is a life threatening complication of an infection. It happens when the body overresponds to infection and releases a lot of inflammatory chemicals into the blood.

These chemicals can trigger the blood clotting process and reduce blood flow to the limbs and internal organs.

Sepsis is more common in infants and people with weakened immune systems.

The symptoms of sepsis include:

  • pinprick or large purple bruising
  • fever
  • pale, clammy skin
  • extreme fatigue
  • chills and shivering
  • rapid breathing

The following are some other possible causes of random bruising on the legs.

Dietary supplements

Although it is rare, some supplements may cause bleeding and bruising.

Supplements that may cause bruising include:

Medications

Some medications may affect the body’s clotting ability and cause unexplained bruising on the legs and other parts of the body.

These medications include:

Physical abuse

Sometimes, random bruising is the result of physical abuse.

Bruising as a result of physical abuse may:

  • be random and not consistent with injury patterns
  • occur in infants who cannot yet walk or crawl on their own
  • cover a large area of the body
  • be in the shape or pattern of a certain object
  • may not match up with the reported injury

To diagnose unexplained bruising on the legs, a doctor will perform a physical examination and ask the person about whether or not they have a family history of bruising.

They will also ask about any other symptoms the person is experiencing and whether or not they are taking any medications or supplements.

The doctor may also perform other diagnostic tests, including blood tests, to rule out any serious underlying causes of bruising.

A person who experiences frequent unexplained bruising on the legs should make an appointment to see their doctor.

This is especially important if the bruising is:

  • significant
  • frequent
  • long lasting
  • very painful to the touch
  • due to medication or supplement use
  • in the same location every time
  • serious despite being due to a small injury or bump

People who frequently experience unexplained bruising on their legs because of their age, sex, or family history should take care to prevent bumps and falls, if possible.

However, if the bruising is the result of taking specific medications or supplements, stopping them could eliminate further bruising. It is vital to speak to a doctor before stopping any medications.

Learn more about home remedies for treating bruises here.

Some people may bruise more easily than others, and unexplained bruising on the legs is likely a case of a minor injury that the person forgot about.

However, if bruising happens frequently, is severe, and takes a while to heal, it may be a symptom of an underlying condition that needs medical attention.