Blood clots look different depending on where they form. On the skin’s surface, a clot typically appears as a red or reddish-brown area that feels raised, firm, and warm to the touch. Deeper clots you can’t see directly, but they cause visible changes like swelling, skin discoloration, and tightness in the affected area. Here’s how to identify what you’re looking at in the most common situations.
Blood Clots vs. Bruises
This is the most common source of confusion, and the differences are straightforward once you know what to look for.
Bruises change color as they heal. They start purple or dark blue, then shift to green, yellow, and eventually fade. A blood clot stays red or reddish-brown and doesn’t cycle through those color stages. The texture is different too: bruises lie flat against the skin, while a blood clot feels raised and rope-like under the surface. Pressing on a clot usually causes sharper, more localized pain than pressing on a bruise.
Swelling is another reliable marker. Bruises cause minimal swelling, but a blood clot often makes the surrounding area visibly puffy and tight. The skin over a clot also feels warm or hot, while a bruise doesn’t change the skin’s temperature. If you notice a discolored area on your leg that’s swollen, warm, and firm rather than flat and color-shifting, that pattern points more toward a clot than a simple bruise.
Clots in the Legs (Deep Vein Thrombosis)
Deep vein thrombosis, or DVT, forms inside the larger veins of the leg. You can’t see the clot itself, but it produces a distinct set of visible and physical changes. The skin over the affected area often turns red or purple, depending on your natural skin tone. In people with darker skin, the color change may appear more as a deepening of the skin’s normal shade rather than an obvious redness.
The leg typically swells, sometimes significantly, and the swollen area feels warm. Pain and tenderness concentrate along the path of the vein, often in the calf. In some cases, especially if the clot is large, the entire lower leg looks noticeably bigger than the other side. This asymmetry, one leg visibly larger than the other, is one of the most telling visual signs.
Over time, if a clot damages the vein, it can cause a longer-term condition where the skin develops persistent discoloration, ongoing swelling, and eventually open sores. This is called post-thrombotic syndrome and represents lasting changes to the vein and surrounding tissue.
Clots Near the Skin’s Surface
Superficial thrombophlebitis is a clot that forms in a vein close to the skin, often in the arms or legs. These are the most visible type because the affected vein sits right beneath the surface. You’ll see a red or discolored streak along the path of the vein, and the area swells, feels hot, and hurts. The vein itself may feel like a firm cord or rope under the skin rather than its usual soft, compressible texture. The redness and swelling can appear suddenly and spread along the length of the vein over hours or days.
Clots After a Tooth Extraction
After a tooth is pulled, a blood clot forms in the empty socket to protect the bone and nerves underneath. A healthy clot looks like a dark, reddish-brown scab sitting in the socket. It should stay in place and gradually shrink as the tissue heals beneath it. If the clot dislodges or dissolves too early, a condition called dry socket, you’ll see a whitish bone visible in the socket instead of that dark protective layer, and the pain intensifies sharply.
Menstrual Blood Clots
Passing small clots during your period is normal. They look like dark red or deep maroon jelly-like blobs and are made of blood and uterine lining tissue. Small clots, anything smaller than a dime, are generally not a concern. The CDC uses a quarter as the threshold: if you’re regularly passing clots the size of a quarter or larger, that’s considered a sign of heavy menstrual bleeding worth investigating.
What Clots Look Like on the Inside
If you’ve ever seen a medical image of a clot and wondered about its color, there’s a reason clots look different in different contexts. Clots that form in veins (like DVT) are rich in red blood cells, giving them a dark red appearance. Clots that form in arteries contain more platelets and a protein called fibrin, making them appear paler, almost white or grayish. Doctors sometimes refer to these as “red clots” and “white clots,” and the distinction matters for treatment because they respond differently to medications.
How Clots Look on Ultrasound
When doctors suspect a clot, they typically use ultrasound to confirm it. A fresh clot appears as a dark mass inside a vein that looks swollen, often wider than the artery next to it. The key diagnostic test is simple: the technician presses the ultrasound probe against the vein. A healthy vein compresses flat like a garden hose. A vein with a clot inside it won’t compress.
As a clot ages, its appearance on ultrasound changes. A clot that’s been there for weeks starts to brighten on the image and the vein returns toward its normal size. An old, chronic clot shows up as a bright, web-like scar attached to the vein wall, and the vein itself may actually be smaller than normal because of permanent scarring. These differences help doctors estimate how old a clot is, which guides treatment decisions.
When a Clot Reaches the Lungs
A pulmonary embolism happens when a clot, usually from the leg, breaks free and travels to the lungs. You can’t see the clot itself, but the body shows distress in visible ways. The skin may turn pale, clammy, or take on a bluish tint, particularly around the lips and fingertips. This bluish color signals that the blood isn’t picking up enough oxygen. Sudden shortness of breath, chest pain that worsens with breathing, and a rapid heartbeat accompany these visible changes. This is a medical emergency.