A bruise occurs when a physical impact breaks small blood vessels beneath the skin’s surface. Red blood cells leak into the surrounding tissue, forming a visible mark. This collection of pooled blood, or hematoma, must be cleared away through the body’s natural healing process. It is common for this damaged area to develop an uncomfortable itch, or pruritus, as the body works to repair the injury.
The Healing Mechanism That Causes Itching
The itch sensation is a direct consequence of the body’s inflammatory and cleanup process following the initial injury. When cells are damaged, mast cells release a chemical called histamine into the area. Histamine increases blood flow to aid healing and directly activates specific nerve endings in the skin, which the brain interprets as an itch.
The cleanup phase also contributes significantly to persistent itching. As the body breaks down the red blood cells, a pigment called bilirubin is released into the tissue. High concentrations of bilirubin can trigger pruritus, acting as a chemical irritant that heightens the itch response.
A separate factor in the itching sensation is the repair of the sensory nervous system. Trauma can temporarily damage the fine nerve fibers that transmit itch and pain signals. As these sensory nerves regenerate and regrow into the healing tissue, they can become hypersensitive or “misfire.” This nerve regeneration can manifest as tingling, crawling, or persistent itching.
Bruise Color Changes and the Healing Timeline
The visible color progression of a bruise maps the biochemical breakdown of hemoglobin, the oxygen-carrying protein in red blood cells. Initially, a fresh bruise appears red or dark purple. Within a few days, the bruise darkens to blue or black as the hemoglobin deoxygenates and begins to degrade.
The appearance of green and yellow hues signals the middle and late stages of healing, often coinciding with the peak of the itching sensation. Hemoglobin is converted first into the green pigment biliverdin, and then into the yellow-brown pigment bilirubin. This green-to-yellow phase, typically five to ten days after injury, represents the body’s most intense period of metabolic cleanup.
Itching becomes noticeable during this phase because the body is actively mobilizing immune cells to clear the bilirubin and other waste products. Once the bruise turns a light yellowish-brown and begins to fade, the breakdown products have been reabsorbed, and the itching usually subsides. Most bruises disappear within two weeks.
Relief Strategies for Itchy Bruises
Managing the itch involves calming the local inflammatory response and keeping the skin barrier healthy. Applying a cool compress (not ice directly) for short intervals can help numb the nerve endings transmitting the itch signal. Cooling also dampens the inflammatory release of histamine by slightly reducing local circulation.
Keeping the skin moisturized is an effective strategy, as dry skin is more prone to itching. Applying a gentle, scent-free moisturizing lotion helps maintain the skin’s barrier function and reduces irritation. Over-the-counter topical anti-itch creams, such as those containing hydrocortisone, can be used sparingly to suppress the local inflammatory response.
It is important to resist the urge to scratch the area. Scratching can further damage the skin, potentially introducing bacteria and increasing the risk of secondary infection. If the itch is severe and persistent, an oral antihistamine may provide relief by blocking activated histamine receptors.
Identifying Abnormal Symptoms
While itching is generally a normal sign of healing, certain accompanying symptoms suggest medical consultation is necessary. Signs of localized infection include increased pain, warmth, or swelling that does not improve after the first few days. The presence of red streaks radiating away from the bruise or visible pus also warrants immediate attention.
A bruise that does not begin to fade or is still present after two weeks, or one that reappears without a new injury, should be evaluated by a healthcare provider. Prolonged healing might indicate a larger underlying collection of blood, known as a hematoma, or another issue.
Systemic symptoms accompanying a bruise are red flags. These include unexplained fever, widespread rash, or unusual bleeding from sites like the gums or nose. Furthermore, any bruise that appears with no clear memory of injury, especially if it is large, frequent, or located on the trunk, may suggest an underlying condition affecting blood clotting.