Blister Under Your Toenail? Here’s How To Treat It

Runners’ feet can be pretty gnarly. Between black or bruised toenails, blisters, calluses, and athlete’s foot, almost every runner would be a good candidate for a pedicure any day of the week.

A blister under your toenail is one of the many common foot maladies you may contend with as a runner. Most of the time, a black toenail actually results from a blood blister under your nail from running, which may or may not pop and spread the blood under the entire toenail. 

If you’re in the large group of runners desperately seeking quick advice and best practices for “a blister under your toenail from running,” rest assured we have you covered. 

In this guide, we will discuss how you get a blister under your toenail from running and how to treat a blister under your toenail to ensure you don’t miss out on training.

We will look at: 

  • What Does A Blister Under Your Toenail From Running Look Like?
  • What Causes A Blister Under Your Toenail?
  • Factors That Increase the Risk of A Blister Under Your Toenail from Running
  • How to Treat A Blister Under Your Toenail From Running
  • Preventing A Blister Under Your Toenail from Running

Let’s get started!

A blister under a toenail where the nail has turned purple.

What Does A Blister Under Your Toenail From Running Look Like?

We’ve all seen a blister at one time or another. They usually look like small, fluid-filled sacs with clear fluid inside the bubble formed by the outer layers of skin. 

The clear fluid inside a regular blister is called serum.

Blisters under toenails from running can take on a couple of different forms.

Some runners get the classic clear bubble blisters at or around the edges of a toenail. They will look like pretty much any blister you’d see on your body; only the blister will be at least partially under the toenail. 

The edge of the nail where you trim it shorter may be slightly raised or pulling up away from the nail bed underneath, and you might notice puffiness in the area of the blister where it extends to your skin in the cuticle or outside of your toenail.

Some blisters under toenails are blood blisters, which means that the fluid inside the blister is blood instead of clear serum. 

The entire toenail may appear black, blue, or bruised, depending on the size, shape, and status of the blood blister, or there may be a distinct blood blister under your toenail where just that region is either dark red, blue, purple, or black. 

In the latter case, the blood blister under your toenail has not yet ruptured.

Blood blisters under the toenails from running are actually so common that they’ve earned a nickname—Runner’s Toe—which is often used in common parlance in place of the medical term, subungual hematoma.

A person cutting their toenails.

What Causes A Blister Under Your Toenail?

Regardless of where they are on your body, most blisters are caused by friction against the skin, and blisters under the toenail can be caused by friction as well.

Even though it’s hard to imagine that there would be friction under a toenail, there actually can be friction or shearing of the skin under the toenail—called the nail bed—relative to the toenail on top. 

Toenails are attached to the nail bed, which is the fragile skin underneath the toenail. 

When you run, if your toenails bump up against the front inside edge of your running shoe or the top of the shoe, the toenail can get pushed towards your body, which moves the toenail and nail bed skin towards you.

However, the bones in your toes are moving forward as you run. This results in a stretching and shearing force on the fragile nail bed skin from the toenail and the toe, moving in opposite directions. 

As your steps accrue while you run, this repetitive shearing and stretching can cause a blister under your toenail.

A pair of pink running shoes.

Factors That Increase the Risk of A Blister Under Your Toenail from Running

In most cases, you can prevent blisters under your toenails from running by wearing the right footwear, but there are additional risk factors that can make you more prone to getting a blister under your toenail.

The following factors can increase the risk of getting a blister under your toenail when you run:

  • Wearing running shoes that are too big, which allows your foot to slide around
  • Running with toenails that are too long
  • Running in damp socks or socks that don’t wick moisture
  • Claw toes or hammer toes, which are toes that are severely curled or bent so that you bear weight on the tips of your toes (in which case, you may have blisters on the tips of your toes and under the top edge of your toenail)
  • Thick or fungus-infected toenails
A hammer toe.

How to Treat A Blister Under Your Toenail From Running

The best way to treat a blister under your toenail from running depends on the location of the blister.

For clear blisters or blood blisters that are around the tip of your toe or edges of your toenail, it’s best to leave the blister alone and allow it to run its course.

However, if the blister is bothering you, you can take a sterilized needle and pop the blister to release the fluid and reduce the pressure underneath your toenail. 

Then, if possible, soak your foot in warm salt water for 15 minutes. Fully dry your foot, and then apply antibacterial ointment and a sterile bandage.

If the edges of the blister are fully confined under the toenail so that you can’t reach a sterile needle into the blister to release the fluid, you’ll need to drill a hole through your nail.

This is best done by a medical professional, though some runners do DIY toenail drilling with sterile hypodermic needles. We don’t necessarily recommend this practice.

Alternatively, although you won’t get the same immediate release you would get some lancing a blister under your toenail, it can be helpful to soak your foot in warm salt water when you have a blood blister. 

This can soften the skin and reduce the risk of infection.

A person soaking their feet in warm water.

Preventing A Blister Under Your Toenail from Running

Ultimately, the old adage, “An ounce of prevention is worth a pound of cure,” certainly applies here.

The best way to prevent blisters under your toenails is to keep your toenails even and short with clean edges and to wear running shoes that fit properly

You want your shoes to have enough length so that your toenails aren’t hitting the end of the shoes, especially when you run downhill, but not so big that your feet are moving around in the shoes.

Work with a shoe fit expert at your local running shoe store to find the right size, and consider an alternate lacing pattern to keep your feet from moving around in the shoes as you run.

Finally, vary your terrain and avoid excessive downhill running. Repetitive motion increases the risk of blister formation, and downhill running increases the shearing between your toenails and nail bed.

Have you had a blister under your toenail? Let us know how you handled it!

To get your running shoes right, use our running shoes guide to find your perfect match.

Two people running on a downhill trail.
Photo of author
Amber Sayer is a Fitness, Nutrition, and Wellness Writer and Editor, and contributes to several fitness, health, and running websites and publications. She holds two Masters Degrees—one in Exercise Science and one in Prosthetics and Orthotics. As a Certified Personal Trainer and running coach for 12 years, Amber enjoys staying active and helping others do so as well. In her free time, she likes running, cycling, cooking, and tackling any type of puzzle.

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