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Smash Your Finger? Get WMI's Tips on Healing Painful Blood Blisters

Poor Angela. Who can remember what she was angry about, anyway? The 2 of us were putting up our tent after a looong and difficult day of hiking and, as you may know, when you’re at the end of your physical and mental reserves you don’t always conduct yourself well.

Angela was a National Outdoor Leadership School instructor, and she and I (an instructor at the NOLS Wilderness Medicine Institute) were leading a 30-day backpacking course together. Grumpily, she picked up a large rock, placed a tent stake against the hard dirt and raised the rock over her head. With a fast swing—followed by a loud scream—Angela smashed her thumb.

Bad news for her, but another chance for me to teach wilderness medicine!

As the dark, painful subungual hematoma formed on Angela’s thumb I collected the necessaries: 1 first-aid kit, 1 stove and 12 students.

Don’t be thrown by the medical terminology. It’s just a blood blister. Look:

Sub      = beneath
Ungual  = relating to a nail, hoof, or claw
Hemat  = relating to blood
Oma    = in general, a swelling (or a tumor)

Sometimes, when you smash your finger, thumb or toe, blood collects under the nail. If it’s not very painful (this is key!) then you should leave it alone. There is nothing you can do to help a non-painful subungual hematoma, and there is not even a way to predict whether or not the nail will fall off sometime later. Leave it alone!

However, sometimes the pressure of the blood under the nail is very painful. Pressure builds and causes the edges of the blister to tear the sensitive nail bed. Some patients even feel throbbing pain in time with their pulse. For a painful subungual hematoma, depressurize it following this procedure:

Subungal hemtoma, cleaned

Step 1: Clean the nail with soap and water, or an alcohol swab.


Step 2: Heat to glowing-red a small piece of metal. Excellent choices include a large needle or a straightened paperclip. Note: The metal must be glowing red hot! It’s a smart idea to wear leather gloves or something to protect yourself from the hot metal—you don’t want to be burned.


Step 3: Gently, quickly touch the glowing red metal to the nail, at the center of the discolored area. Careful! You only want to melt through the nail. Do not push through so far that you injure the nail bed.


Step 4: Expect a quick squirt of blood and fluid. Clean this up, and then cover the perforated nail with an adhesive bandage. Soon the hole will plug itself with a clot, and your patient should be able to return to everyday activities.

Angela’s thumb provided a very satisfactory show for our students, and her pain was resolved. After some rest, a nice hot drink and a nutritious dinner, Angela felt like her old self again.

For another view, here is a decent video of the procedure.

Better yet, if you want to see me demo it, and learn tons more, sign up for a 2-, 3-, 5-, 10- or 30-day course from NOLS Wilderness Medicine Institute. Our wilderness medicine courses cover everything from airway management to zoonosis. Learn and practice what to do in any wilderness emergency. Visit us at to sign up today.

Posted on at 11:00 AM

Tagged: NOLS, Wilderness Medicine Institute, blood blister, subungual hematoma and wilderness medicine

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