That firm lump you’re feeling beneath a bruise is almost certainly a hematoma, a pocket of blood that has collected under the skin after an injury. When a hit or impact damages blood vessels, blood sometimes pools into a contained mass rather than spreading thinly through surrounding tissue. This pooled blood pushes outward against skin and muscle, creating a noticeable lump that feels distinctly different from the tissue around it.
How a Hematoma Differs From a Regular Bruise
A standard bruise happens when tiny blood vessels break and blood seeps into surrounding tissue in a diffuse, spread-out way. You see discoloration, but the area stays relatively flat. A hematoma forms when the bleeding is more substantial and the blood collects in one spot rather than dispersing. That concentrated pool creates pressure, which is why you feel a raised, sometimes firm or rubbery lump beneath the skin’s surface.
Hematomas can form at different depths. A subcutaneous hematoma sits just beneath the skin and is the most common type you’d notice after bumping into something or taking a fall. You can usually see the bruise clearly and feel the lump right under it. Intramuscular hematomas form deeper, within the muscle itself. These tend to be more painful, can limit your range of motion, and sometimes aren’t visible on the skin’s surface at all because the blood is too deep to show through.
What the Lump Feels Like
In its early stages, a hematoma lump typically feels soft or spongy, like a small water balloon trapped under the skin. Over the following days, it often firms up as the blood begins to clot. Some people describe it as feeling like a hard knot or a marble. The area around it is usually tender, warm, and swollen. The overlying bruise will cycle through the familiar color changes (red to purple, then greenish-yellow) as your body breaks down the trapped blood.
The size varies widely. Some hematomas are pea-sized, while others can spread across several inches if the initial impact was significant. Larger ones tend to take longer to resolve and may feel more uncomfortable as they put pressure on surrounding tissue.
How Long It Takes to Heal
Most small hematomas reabsorb on their own within one to four weeks. Your body gradually breaks down the clotted blood and carries it away through the lymphatic system. As this happens, the lump shrinks, the bruise fades, and the tenderness decreases. Larger or deeper hematomas can take considerably longer, sometimes two months or more, to fully resolve.
During the healing process, you may notice the lump changes texture. It might go from soft to firm, then gradually soften again as the body reabsorbs the blood. This is normal progression, not a sign that something is wrong.
What Helps It Heal
For the first 48 to 72 hours, applying ice wrapped in a cloth for 15 to 20 minutes at a time can help reduce swelling and slow any continued bleeding into the area. Keeping the injured area elevated above your heart when possible encourages fluid drainage. Gentle compression with a bandage can limit further swelling, though it shouldn’t be tight enough to cause numbness or tingling.
After the initial few days, some people find that gentle warmth helps the body reabsorb the blood faster by increasing circulation to the area. Avoid massaging the lump aggressively, especially in the first week, as this can worsen bleeding or irritate the tissue. Over-the-counter pain relievers can help with discomfort, but avoid aspirin and ibuprofen in the first day or two since they thin the blood and may increase bleeding.
When a Lump Under a Bruise Needs Attention
Most hematomas are harmless and resolve without medical treatment. But certain signs suggest the lump needs evaluation. If it keeps growing larger over several days rather than stabilizing or shrinking, that could mean active bleeding is continuing. A lump that becomes increasingly painful, red, or warm to the touch may indicate infection, especially if you develop a fever.
Any hematoma that persists beyond four to six weeks, increases in size after the initial swelling period, or develops unusual characteristics should be evaluated with imaging. Ultrasound is typically the first choice for assessing soft tissue lumps and can confirm whether you’re dealing with a straightforward hematoma or something that needs further investigation. In cases where the ultrasound findings are unclear or there’s any concern about a deeper issue, MRI provides a more detailed look and can distinguish a hematoma from other types of soft tissue masses.
Numbness, tingling, or loss of movement near the injured area are more urgent signs. These could indicate the hematoma is pressing on nerves or restricting blood flow, particularly in areas like the forearm or lower leg where tissues are tightly packed.
The Rare Risk of Calcification
In uncommon cases, a hematoma that forms within muscle tissue can trigger a process where the body deposits calcium and eventually forms bone-like tissue inside the muscle. This condition, called myositis ossificans, occurs in roughly 75% of cases after a documented trauma. Instead of the lump softening and disappearing over time, it hardens permanently.
What happens is that the injury triggers an inflammatory response that essentially confuses the body’s repair system. Cells that would normally rebuild muscle tissue get redirected toward producing bone. The result is a hard, sometimes painful mass within the muscle that can limit movement. This is more likely after severe impacts, repeated injury to the same area, or if a deep hematoma is aggressively massaged too early in the healing process.
If you notice that a lump is getting harder rather than softer after several weeks, or if stiffness and limited motion are getting worse instead of better, imaging can determine whether calcification is developing. Caught early, most cases improve with rest and physical therapy. Established bone deposits occasionally need surgical removal if they significantly affect function.
Hematomas Without an Obvious Injury
If you’ve found a lump under a bruise and can’t recall any injury, it’s worth paying closer attention. Spontaneous hematomas, those that form without trauma, are less common but can signal underlying issues like a bleeding disorder, medication side effects (particularly blood thinners), or in rare cases, a vascular problem. These tend to occur more often around the abdomen and torso. Spontaneous muscle hematomas carry a significantly higher complication rate than those caused by a known injury, so unexplained lumps that appear without a clear cause deserve a medical evaluation rather than a wait-and-see approach.