You’re staring at it. It’s dark, almost purple or black, and it looks like a tiny, angry grape stuck under your skin. Honestly, the first time most people see a blood blister, they freak out just a little bit. It isn't like a normal friction blister that’s clear and fluid-filled. This looks different. It looks "medical." But usually, it’s just your body's way of saying you pinched your finger in a door or wore the wrong shoes for a five-mile hike.
Looking at images of a blood blister can be a bit of a rollercoaster. You’ll see some that are tiny pinpricks on a fingertip and others that are massive, dark welts on the heel of a foot. The color is the giveaway. While a standard blister is filled with serum—a clear, yellowish fluid—a blood blister happens when the dermal tissues and blood vessels are damaged without the skin actually breaking. The blood gets trapped. It stays there, pools, and creates that distinct crimson-to-black hue that makes everyone reach for their phone to Google what on earth is happening to their skin.
Why the color changes in images of a blood blister
If you scroll through a gallery of these things, you'll notice the colors aren't consistent. A fresh one is bright red. It’s vibrant. That’s because the blood is still oxygenated and newly trapped. Give it forty-eight hours. It’ll start to look like a bruise—deep purple, then eventually a crusty, brownish-black. This is totally normal. It’s just the blood drying out and the body beginning the reabsorption process.
Most of these occur on "high-impact" areas. Think hands and feet. A classic example is the "pinch" injury. You’re working on a DIY project, the pliers slip, and snap—instant blood blister. Or maybe you're a runner and your new trainers are rubbing a very specific spot on your pinky toe. In these cases, the sheer force separates the layers of skin, and the capillaries underneath just give up the ghost.
Distinguishing a blood blister from something more serious
This is where things get tricky. People often confuse a blood blister with a "cherry angioma" or, more seriously, subungual melanoma if it’s under a nail. Look closely at the photos. A blood blister is almost always tied to a specific "ouch" moment. You remember the pinch. You remember the friction. If a dark spot appears out of nowhere and doesn't change color or move as the skin grows, that’s when you need a dermatologist, not an internet search.
According to the American Academy of Dermatology, the primary rule for any blister is simple: leave it alone. I know, it’s tempting. You want to poke it. You want to see if it’ll pop like a grape. Don't. That skin on top is a sterile, natural bandage. The moment you break it, you’re inviting every bacterium on your skin to a party inside your wound.
The anatomy of the "pinch" injury
It’s basically physics. When the skin is pinched but not torn, the pressure breaks the tiny blood vessels (capillaries) in the dermis. The blood leaks out but has nowhere to go because the epidermis—the tough outer layer—remains intact. This creates a pressurized pocket. It hurts. It hurts because that extra fluid is pushing against nerve endings that aren't used to having a roommate.
If you look at high-resolution images of a blood blister on the palm of a hand, you can sometimes see the "roof" of the blister is thicker than one on, say, the inside of your cheek. Oral blood blisters (angina bullosa haemorrhagica) are a whole different beast. They happen fast, usually while eating something crunchy like crusty bread or chips, and they pop almost instantly because the mucosal lining is so thin.
Treatment: What to do when you’ve got one
So, you’ve confirmed it’s a blood blister. Now what?
First, ice it. Cold constricts the vessels and might stop the blister from getting bigger if you catch it immediately after the injury. Wrap an ice pack in a paper towel—don't put raw ice on your skin—and hold it there for ten minutes. It numbs the throb, too.
- Protect the site: Use a moleskin pad or a thick bandage. You want to create a "donut" around the blister so nothing actually touches the raised part.
- Keep it clean: If it does pop on its own, treat it like an open wound. Wash with mild soap and water.
- Avoid "Home Surgery": Seriously, put the needle down. Unless it’s so large it’s preventing you from walking, there is zero medical reason to drain it at home.
When images of a blood blister look "wrong"
Nuance matters here. A standard blood blister should start to flatten out within a week. If you’re looking at yours and it’s surrounded by a spreading red "aura," or if there are red streaks leading away from it, that’s a red flag. That’s a sign of lymphangitis or a spreading infection. If the fluid inside starts looking cloudy or like pus (yellow/green), the "blood" blister has become an infected one.
There’s also a condition called "black heel" (talon noir). It’s common in basketball players or tennis players who do a lot of lateral stopping and starting. It looks like a massive, flat blood blister or even a suspicious mole. In reality, it’s just repeated micro-trauma causing blood to leak into the topmost layer of the skin. It’s harmless, but it looks terrifying in a zoomed-in photo.
The "Under the Nail" Dilemma
Subungual hematomas—blood blisters under the fingernail or toenail—are the most painful version. The nail is rigid. When blood pools under it, the pressure has nowhere to go. In images, these look like a black or blue smudge under the nail plate. If the pain is "I can't sleep" bad, a doctor might perform "trephination," which is just a fancy word for poking a tiny hole in the nail to let the pressure out. Do not try the "hot paperclip" trick you saw on a 90s action movie. Just don't. You'll end up with a secondary infection or a burned nail bed.
Final reality check for your skin
Skin is resilient, but it’s also a giant signaling system. Most blood blisters are just "oops" marks. They tell the story of a door that shut too fast or a shoe that was half a size too small. They heal from the bottom up. As new skin forms underneath, the old, dried blood gets pushed to the surface and eventually just flakes off. It's kinda gross, honestly, but it’s a sign of a working immune system.
If yours hasn't changed in three weeks, or if it’s in an area that wasn't injured, see a pro. Otherwise, keep it padded, keep it dry, and let your body do the heavy lifting.
Actionable Steps for Recovery:
- Apply a cold compress for 10-15 minutes immediately after the injury to reduce the total volume of trapped blood.
- Elevate the area if the blister is on a foot or hand to help reduce the throbbing sensation and swelling.
- Cushion the blister using a hydrocolloid bandage or a "donut" style moleskin patch to prevent accidental rupture during daily activity.
- Monitor for warmth or increased swelling; if the area feels hot to the touch or you develop a fever, seek medical attention for a potential infection.
- Wait for the "peel"—once the blister has dried and the skin underneath is healed, the dark spot will naturally migrate to the surface and slough off. Do not force this process.