Experiencing random bruises on your legs—or anywhere on your body—can be confusing and frustrating. Sometimes a bruise appears without a clear memory of an injury, while in other cases, even a tiny bump can result in a noticeable mark. Although most unexplained bruising is harmless, certain cases may hint at underlying health conditions.

This guide walks you through what bruises really are, why they show up unexpectedly, and when you should seek medical attention.

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What Is a Bruise?

A bruise forms when small blood vessels under the skin break due to some level of trauma—even a mild one you may not remember. Blood then pools under the skin, causing the familiar blue, purple, or black discoloration. As the bruise heals, it turns green or yellow before fading completely.

Bruises typically heal within 1–2 weeks.

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Common Causes of Random or Unexplained Bruising

1. Aging

As skin gets thinner and loses protective fat, blood vessels become more fragile—making bruising more common, especially on legs and arms.

2. Vitamin Deficiencies

• Vitamin C deficiency weakens blood vessels, causing increased bruising.

• Vitamin K deficiency impairs clotting, making bruises appear easily.

Both deficiencies may also cause petechiae or purpura—tiny red or purple dots under the skin.

3. Medications & Supplements

Blood-thinning drugs such as:

• Aspirin

• Anticoagulants

• Certain antibiotics

…can increase bruising. Herbal supplements like ginkgo biloba, turmeric, ginger, and St. John’s Wort may have similar effects.

4. Hereditary Factors

Some people naturally bruise more easily due to genetics. Women also tend to bruise more than men due to differences in skin and blood vessel structure.

5. Bleeding Disorders

Conditions such as hemophilia or Von Willebrand disease impair clotting and may cause:

• Large or frequent bruises

• Nosebleeds

• Prolonged bleeding

6. Too Much Sun

Long-term sun exposure weakens skin and blood vessels, making the skin more prone to bruising.

7. Intensive Exercise

Strenuous workouts—especially weightlifting—can cause micro-tears in blood vessels and lead to bruising.

8. Diabetes

Poor circulation from diabetes may cause bruising that heals slowly or appears unexpectedly. This often occurs alongside increased thirst, urination, and fatigue.

9. Viral Infections

Certain infections can lower platelet counts (thrombocytopenia), leading to unexplained bruising. Examples include:

• Chickenpox

• Mumps

• Rubella

10. Autoimmune Diseases

Conditions like lupus, rheumatoid arthritis, and vasculitis can trigger inflammation in blood vessels, causing unexplained bruises.

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More Serious but Less Common Causes

Liver Disease

Impaired liver function reduces clotting factors, leading to unexplained bruising, yellowed skin, and swelling.

Kidney Disease

Late-stage kidney disease may cause easy bruising along with fatigue, numbness, or changes in urination.

Cancer

Chemotherapy and blood cancers like leukemia can cause:

• Frequent bruises

• Tiny red spots (petechiae)

• Fatigue

• Weight loss

An unexplained bruise on the breast that doesn’t heal may be a sign of inflammatory breast cancer.

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When to See a Doctor

Seek medical evaluation if:

• Bruises don’t heal within 2 weeks

• New bruises appear suddenly or frequently

• You notice bruising for no clear reason

• The bruise is extremely painful

• There are signs of infection

• Bruising occurs with nosebleeds, bleeding gums, or unusual fatigue

• The bruise appears with neurological symptoms or swollen limbs

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Natural Remedies to Help Bruises Heal Faster

You can reduce inflammation and shorten healing time using:

• Cold compresses

• Aloe vera

• Arnica gel

• Witch hazel

• Vitamin C-rich foods

• Gentle elevation and rest