You can't help but cringe when you see one.
And you certainly don't want these to be yours!
It pays to have a healthy respect for blood blisters as they pose a heightened risk for infection. Particularly for trail runners and during multiday races.
But do you know what makes a blood blister?
And how do you deal with them? Do you pop them or not?
What causes a blood blister?
The presence of blood in a blister indicates there is high pressure component. This high pressure causes deeper injury - injury to small blood vessels in the dermis. Blood then tracks into the epidermis and mixes with the normal blister fluid. That's why blood blisters often occur over joints and bony prominences: like the back of the heel, the toes and the metatarsal heads (ball of the foot).
What colour are blood blisters?
In the initial stages, a blood blister looks red. Then as the blood dries and coagulates over time, is goes a purple or black.
How long does a blood blister take to disappear?
Blood stains the skin cells it comes in contact with. It can take a month or more for that discolouration to disappear. We know it takes somewhere from 30 to 48 days for full epidermal cell turnover - that is for cells to travel from their deepest to most superfical, to be shed as dead skin cells. So it could take that long before all trace disappears. The blood will dry relatively quickly, assuming you take away the cause. If you don't deal with the cause, your blood blister will last longer.
There may be a lot of black dried blood that flakes away. Or there may be just a little.
- It depends on how much blood there was initially.
- It depends on how much of the blood resorbed.
- And it depends on whether you reduce the excess pressure or not - it may be a perpetual blood blister if you don't do anything to stop it from forming.
Cause and Prevention
Structural causes of blood blisters
Bony prominences are at most risk, like a bunion for example. Having a bunion makes the forefoot wider. It's not necessarily the bunion itself at most risk of developing a blood blister. The weightbearing undersurface is - as the prominent joint bulges over the sole of the shoe. This provides a concentration of pressure. Coupled with high friction, there's a blood blister waiting to happen.
Biomechanical causes of blood blisters
The blood blisters under the big toes in the first image of this article are a consequence of the foot's biomechanics. There's an important function of the 1st MPJ (big toe knuckle) called the windlass mechanism. When it's not working adequately, there can be extremely high pressure under the joint of the big toe - where these blisters are.
The best way to deal with this is with to see a Podiatrist because they know how to facilitate the windlass mechanism - treatment will likely include orthotics and calf stretches and maybe some other things, depending on where you're getting blood blisters.
If you miss the blister prevention boat and end up with a blood blister, do all the normal things for blister treatment. But now, preventing infection really is your priority! Consider the options below, depending on your blister location, the environment you're in and what gear you have access to.
1) Take away all pressure
If it's possible, remove all pressure to ensure the blister roof remains intact and allow it to heal in its own time. For the blood blister on top of your toe, simply wearing open-toed sandals might work. Or open-backed scuffs for heel blisters. Barefeet or complete nonweightbearing may be your only option, depending where your blood blister is. By taking away all pressure, the blister remains intact with no chance of infection.
But if your blood blister is on the weightbearing area of the foot, or you have to wear shoes, it's not quite so simple.
2) Reduce some pressure and cut friction levels
There are parts of your foot where taking away all pressure might not be possible - like under the ball of the foot. And there are times when you just have to keep going. This is where pressure deflection can help in conjunction with reducing friction levels. Thick adhesive orthopedic felt can be cut into "donut pads" with the blister positioned in the cavity to take pressure off it. And before you do anything else, read this about reducing friction to treat blisters.
I would use much thicker felt than that pictured below.
Popping Your Blood Blister
There are times when keeping the blister roof intact is not the best option. It can be better to take matters into your own hands rather than ignore it and simply hope for the best. If you have the right equipment, you could deal with this appropriately and safely. It sure beats putting your blood blister with roof intact back into your shoe with no dressing and no pressure relief and just leaving it to chance.
If the amount of blood accumulating is causing pain; if the blister is too big and likely to tear; if you have to carry on running or hiking; it may be best to lance it. I would probably lance that blood blister on the top of the 4th toe pictured above. But you must realise the increased risk of infection. Remember, it is OK to not lance your blood blister. If in doubt, don't pop it! Read this article to help you decide if to lance or leave alone.
If you are going to lance your blister, you need to do it in a clean environment using clean techniques. To do this, you'll need certain equipment.
- Clean your hands and foot (soap and water or antibacterial hand gel)
- Lance with a sterile implement (sterile scalpel blade or needle)
- Apply antiseptic (betadine) and dress with a sterile dressing
- Remove or deflect pressure
- If you want your blister to heal as quickly as possible, you've also got to cut friction levels.
- Then you need to keep it clean and monitor over the coming days for signs of infection. If you suspect there is infection, seek medical help.
Please realise the risk of bacterial infection. For the following few days, you'll need to be on the watch for signs of infection which include redness, swelling, pain and pus. And if you notice red streaks extending from your blister up your leg, this is serious and you need urgent medical attention.
- Get the pressure off (or down)
- Speed healing by reducing friction!
- Be clean, use antiseptic and a sterile non-adherent dressings to protect from infection
- Don't just ignore it and keep going or it will tear and be open to infection
- Don't ignore the benefits of lancing it (but only if the situation is right!)
- Don't neglect pressure relief and friction relief
Written by Rebecca Rushton
Rebecca is an Australian podiatrist with over 20 years experience. She has spent a lifetime dealing with her own blister prone feet in her sporting and everyday life. Rebecca specialises in helping athletes and sports medicine professionals figure out how to manage foot blisters with ease. And for kicks, she enjoys providing blister care at multiday ultramarathon events.
Rebecca is the founder of Blister Prevention and author of "The Blister Prone Athlete's Guide To Preventing Foot Blisters".