What Causes Unexplained Bruising on the Legs or Elsewhere on the Body?

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Random bruises, also referred to as contusions, may happen without a clear cause or injury. Some people may be more susceptible to random bruising than others, especially if they have a condition that makes them bruise easily.

Bruising occurs when there is an injury to tissues underneath the skin. This can damage blood vessels and causes blood to pool below the surface of the skin, leaving behind black, blue, purple, brown, green, or yellow marks.

Bruises aren’t typically something to worry about, and they tend to heal on their own in a few days or weeks. However, you may want to see a healthcare provider to determine why you have unexplained bruising.

This article discusses risk possible causes of unexplained bruising, how to treat random bruising, and when to seek medical attention.

Midsection Of Woman With Bruise On Arm

Sharon Mccutcheon/ EyeEm / Getty Images

What Are the Risk Factors for Random Bruising?

There are various risk factors associated with random and easy bruising, such as genetics, age, and sex.

While there's no evidence of a specific genetic component that drives random bruising, studies have shown that people who bruise easily often have close family members who do as well.

When a person bruises easily, they may experience random and unexplained bruises from everyday activities and events that would typically not affect someone else. For example, they may get a black-and-blue after gently knocking their leg against a desk.

A person with fairer skin and fragile blood vessels, genetic traits, can make bruises develop more easily and appear darker in color.

On top of genetics, aging can be a factor of unexplained bruising. Older adults often experience random bruising as part of the natural aging process. This is due to weakening blood vessels that are more prone to breakage even with slight injury to the area.

Sex can also affect bruising, as those born female tend to bruise more easily than those born male.

What Causes Random Bruising?

There are several causes that may lead to unexplained bruising, like certain medications, nutrient deficiencies, and medical conditions.


Some medications can lead to easy or random bruising because of how they affect the body. Specific medications include:

  • Nonsteroidal anti-inflammatory drugs, like Advil (ibuprofen) or Aleve (naproxen)
  • Blood thinners, such as aspirin and Coumadin (warfarin): Your blood naturally clots to prevent excessive bleeding related to an injury. Blood thinners prevent this clotting, which means minor injuries can cause excessive pooling of blood underneath the skin that leads to bruising.

Bleeding Disorders

Bleeding disorders occur when the blood doesn’t clot as it should. There are several different bleeding disorders that can cause a person to bruise randomly, including:

  • Hemophilia A and B: Both hemophilia A and hemophilia B occur when the blood doesn’t clot properly. Hemophilia A is a genetic condition, while hemophilia B develops when a person is missing a specific factor (factor IX) that encourages proper blood clotting.
  • Von Willebrand disease: This is an inherited bleeding disorder that also causes issues with blood clotting.

Nutrient Deficiency

Nutrients are important for all bodily functions, and not getting enough vitamins and minerals can cause various health issues. Unexplained bruising is one of them.

There are several nutrient deficiencies associated with easy or random bruising, including:

  • Vitamin C: Vitamin C is important for many reasons, one being wound healing. Without enough vitamin C in the body, random bruising can occur.
  • Iron: Iron is vital for healthy blood cells because it aids in the delivery of oxygen throughout the body. Without adequate oxygen, skin becomes more likely to bruise.
  • Vitamin K: Vitamin K plays a role in blood clotting. Without enough vitamin K, blood clots don’t form as quickly, leading to more blood under the skin, and thus, a bruise.

Vitamin C Deficiency and Leg Bruising

Although vitamin deficiencies can lead to random bruising across the entire body, one case report found the bruising to be localized to the legs.


Diabetes is a chronic condition that develops because of the body’s inability to produce or use insulin, a hormone designed to manage blood sugar levels.

The condition can lead to bruising that lasts longer than normal because of the way it affects wound healing.

Low Blood Platelets

Blood platelets are specific cells that exist within the blood. When certain blood vessels are damaged, blood platelets bind together to repair the issue.

People with low counts of blood platelets often bruise easily because there are fewer platelets in the blood to repair damaged blood vessels. A low platelet count is also called thrombocytopenia, and there are a few potential causes, such as:

  • Certain cancers, including leukemia and spleen cancer
  • Chemotherapy drugs
  • Biological therapies
  • Radiation therapy of the bone marrow or pelvis
  • An enlarged spleen

Cushing's Syndrome  

Cushing's syndrome is a condition that arises when levels of cortisol, a stress hormone, are too high in the blood.

Cushing's causes easy bruising because it can lead to thinning skin.

Ehlers-Danlos Syndrome

Ehlers-Danlos syndromes are a group of hereditary health conditions that negatively affect the function and structure of connective tissues such as the skin, joints, and walls of the blood vessels.

Because of this, easy bruising is often a symptom of Ehlers-Danlos syndrome.

Non-Hodgkin Lymphoma

This is a type of cancer that begins in lymphocyte cells, which are immune cells designed to aid in the fight against pathogens.

If a person has non-Hodgkin lymphoma, especially in their bone marrow, it can reduce blood cell count and blood platelet count, leading to clotting issues and random bruising.

How Are the Causes of Random Bruising Diagnosed?

To determine what's causing random bruising, a healthcare provider will likely do a physical exam and go over your medical history. They may ask you questions about:

  • The circumstances surrounding your bruises
  • Whether you're taking any medications
  • What you typically drink and eat
  • Whether your relatives also randomly bruise or have any conditions that cause random bruising

They may also recommend blood tests, such as a complete blood count (CBC) and a coagulation factor test, which check to see if there's an issue with your ability to form blood clots.

What Is the Treatment for Random Bruising?

In many cases, random bruising doesn’t require any treatment at all and will heal on its own.

If you are in pain because of the bruise, you can apply a cold compress to the area to slow down blood flow. Keeping the bruise elevated above the heart can prevent further blood pooling.

Bruises that are caused by underlying health conditions are addressed by treating the specific condition or disease. Therefore, treatment options will vary widely if you are experiencing bruising because of a health condition. 

When to Call a Doctor

Experiencing random bruising can be alarming, but it doesn’t always warrant a visit to your doctor. That being said, you should see your doctor if:


  • The bruise doesn’t go away
  • You don’t know where the bruises are coming from and they occur regularly
  • The bruise is exceptionally painful

Can You Prevent Random Bruising?

It’s difficult to avoid bruising completely, especially when the cause is unknown.

People that are active should take special precautions while participating in physical activities to prevent injuries that could lead to bruises. This can be done by wearing protective gear while you play sports or engage in other physical activities that could lead to bruising.

For example, you can protect against leg bruising by wearing shinguards when playing soccer or wrapping table legs in protecting padding.

Frequently Asked Questions

  • Do bug bites leave bruises?

    While not everyone will experience bruising after a bug bite, it is entirely possible to develop a small contusion if you get bitten by an insect. It is more commonly associated with specific insects.

  • How long does it take for a bruise to heal?

    Bruises typically heal on their own within two weeks of the initial injury. If you find yourself in pain because of the bruise, you can apply a cold compress and keep the bruise elevated above the heart. This may help speed the healing process because it lowers inflammation and prevents more blood from pooling in the area.

  • Why is my bruise yellow or green?

    Bruises often change colors as they heal. Bruises typically turn yellow or green roughly five to 10 days after your injury and do so because the body produces specific compounds to break down the blood that has gathered in the area. These compounds are known as biliverdin and bilirubin and are actually pigments that occur naturally when they break down blood. When the bruise turns yellow, it’s because more bilirubin is responsible for breaking down the blood and when it turns green, it is the action of biliverdin.

  • Why is my bruise hard?

    Bad bruises, also known as hematomas, can occur following a more serious injury. Along with the discoloration associated with a bruise, hematomas can also cause the area to feel hard or firm to the touch.

13 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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By Angelica Bottaro
Angelica Bottaro is a professional freelance writer with over 5 years of experience. She has been educated in both psychology and journalism, and her dual education has given her the research and writing skills needed to deliver sound and engaging content in the health space.