What Causes Random Bruises on Legs?

Bruises can appear anywhere on the body and for a variety of reasons. Most commonly, they’re due to physical trauma.

When the blood vessels underneath the skin get damaged, they release blood, which causes the skin to look bluish or purplish.

Random bruises on the legs can be an alarming symptom. If you have it, you’re probably worried that it’s something serious.

This article will explore all the possibilities for your mysterious leg bruises.

What is a Bruise?

Let’s briefly talk about what a bruise is, followed by what’s causing it.

A bruise happens when red blood cells (RBCs) leak out of veins and capillaries.

The blood collects underneath the skin, causing the skin to become blackish, reddish, purplish, or bluish. Most bruises go away within 5-10 days.

If your random bruises on leg aren’t going away within that timeframe, then it could be a sign of an underlying medical illness.

The Most Common Cause – Physical Trauma

By far the most common cause of a bruise is physical trauma. Do you play a sport?

Do you participate in strenuous physical activity? Were you recently in a car accident?

Any of these could be the reason for your leg bruise. The good news is that most bruises go away completely within 1-3 weeks.

While rare, it’s possible for a bruise to show up to several days after the physical trauma has taken place. This can make it difficult to pinpoint the exact cause.

UV Radiation

In elderly people, excessive sun exposure can lead to random bruises on your legs.

As the UV rays hit the skin, they begin to break down and thin the walls of blood vessels.

If the blood vessel walls become too thin, they’ll begin to release blood, leading to a bruise.

Most people don’t realize that UV radiation can cause bruising.

Now you know that it can. You can easily fix this by wearing pants. That way, your legs aren’t exposed to the UV rays whenever you go outside.

Certain Medications

The human body is very complex. It’s impossible to know exactly what’s going to happen whenever you take a medication.

Some patients report mysterious bruises on their legs after taking a medication. If this is happening to you, tell a doctor.

They may be able to swap out your medication for another that doesn’t have this side effect.

Medications known to cause leg bruises are ibuprofen and aspirin. Why these? Because they affect platelet function.

Certain corticosteroids can also lead to random leg bruises by causing inflammation.

As tissues become inflamed, the surrounding blood vessels can leak out blood, forming a bruise.

Vitamin K Deficiency

Vitamin K is a fat-soluble vitamin that’s required to stay healthy. Without it, you may develop various problems, such a bruising.

Whenever you eat foods rich in vitamin K, the body stores it within the liver as well as within fat tissue.

The main roles of this vitamin are to help blood coagulate (clot) properly. It also plays a role in bone health.

Foods rich in vitamin K include leafy greens (collards, turnip greens, spinach, kale, etc.) as well as vegetables like broccoli, cabbage cauliflower.

Weight Loss

Have you recently lost a lot of weight? If so, you’re more susceptible to bruising on your legs.

You see, body fat serves an important role: not only does it keep you warm, but it also serves as a cushion against physical trauma.

With reduced body weight, your internal organs and tissues won’t be as protected. This means that less force is needed to cause a bruise.

Use a BMI calculator to determine a healthy weight for your height and activity level.


Diabetes is a disease that results in the over-accumulation of sugar in your blood.

Over time, high blood sugar can lead to neurological problems (and even death).

Random leg bruising isn’t a common symptom of diabetes, but it happens in some people. If you have this symptom, then talk to a doctor.

If left untreated, diabetes can result in serious medical problems, such as amputations.

The sooner you take care of it, the less likely you are to suffer from these complications.

Diseases Related to the Blood

Any disease that relates to the blood can cause excessive bruising. Examples include:

  • Hodgkin’s Disease
  • Leukemia
  • Sepsis
  • Thrombocytopenia
  • Platelet Dysfunction
  • Hemophilia

These diseases require immediate medical attention. Otherwise, they can lead to death.

Aside from leg bruises, you might also experience weakness, fatigue, and unexplained weight loss.


It doesn’t take much force for an older person to get a bruise.

That’s because old people have weakened connective tissue compared to younger people.

If you’re an older individual, be extra cautious about bumping into things.

Something as simple as walking into a desk can result in the formation of a leg bruise. Older people also tend to heal more slowly than younger people.

For example, bruises in older people can take several weeks to heal, while in younger people, they typically heal in less than a week.

How to Treat Unexplained Bruises on Legs 

Here are some ways to treat your symptom:

  • Ice Pack: A cold compress using an ice pack can treat your pain as well as reduce inflammation. The cold will slow down the amount of blood being released from the broken blood vessels as well. Ice the bruise for about 15 minutes per session, and do 3-4 sessions per day.
  • Warm Towel: If you’ve had the bruise for longer than a few days, then a warm/hot compress can help make the bruise disappear faster. Apply a warm/hot towel to the affected area for 15 minutes at a time. Repeat 3-4 times per day until the bruise is gone.
  • Elevation: Random leg bruises can also be treated with elevation. Elevating your leg can help reduce swelling as well as limit the extent of the bruise. There are various ways to elevate your leg. We recommend doing a Google search on how to do it properly.
  • OTC Drugs: When all else fails, give OTC drugs a try. Don’t take aspirin since it inhibits clotting and can make your bruise worse. On that note, don’t use any OTC anti-inflammatory drugs. Acetaminophen is the best choice for treating leg bruises.

When it comes to bruises, time is your best friend. If you just leave it alone, eventually it will go away.

When Should You See a Doctor About Random Leg Bruises?

If your bruise is a one-time event, then you probably don’t need to see a doctor. If it’s a reoccurring issue, then you should schedule an appointment.

Call if your doctor if your bruises are becoming increasingly larger, if you have bleeding gums, or if you’re in extreme pain while taking blood-thinning medication.

Also, if your mysterious leg bruises are increasing in frequency, or if they’re not going away after a week or two, then call your doctor.

While it could be nothing, there’s also a chance it could be diabetes, a vitamin deficiency, or something more serious.

Can Unexplained Leg Bruises Be Prevented?

It depends on what’s causing them. If it’s due to physical trauma or a vitamin deficiency then yes, it can be prevented.

First you need to figure out what vitamin you’re deficient in, and then eat foods (or take supplements) that contain it.

If it’s due to physical trauma, such as playing a contact sport, then wear proper protective gear.

When working on your knees, try to use protective padding to reduce the chance of an injury.

Finally, if you’re an older individual then illuminating your home with nightlights can prevent you from falling during the night.

Ask a Question: If you want to ask a medical doctor a question that hasn't been answered in one of our articles go to: Ask a Medical Doctor About your Symptoms

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