The question of whether melanoma can look like a bruise is a serious concern. While both conditions can manifest as dark, discolored patches on the skin, their origins are fundamentally different. A bruise results from mechanical injury to blood vessels, but melanoma is an uncontrolled proliferation of pigment-producing cells called melanocytes. Understanding these distinctions is essential for protecting your health.
Comparing Appearance, Cause, and Sensation
The most significant difference between a bruise and a melanoma is the underlying cause. A bruise, or contusion, forms immediately following trauma or impact, causing small blood vessels to rupture beneath the skin’s surface. Melanoma, conversely, arises spontaneously from genetic changes within melanocytes, involving no external injury.
Bruises are typically tender, painful, or swollen due to inflammation and pooled blood beneath the skin. In contrast, early-stage melanomas are often painless and may have a surface texture that is raised, nodular, or ulcerated, differing from the flat feel of a fresh hematoma. A key area of confusion is the nail bed, where a subungual melanoma can appear as a dark, vertical streak easily mistaken for a trauma-induced bruise.
The location of the spot can also offer a clue, though this is not definitive. While bruises can appear anywhere, certain high-risk melanomas, such as Acral Lentiginous Melanoma, specifically appear on non-sun-exposed areas like the palms or soles of the feet. A bruise is a temporary injury that will predictably resolve, whereas a melanoma is a persistent, growing lesion.
Characteristics of Harmless Bruises
A harmless bruise follows a predictable healing process involving a sequence of color changes as the body metabolizes the leaked blood. When a bruise first forms, it appears reddish or pink due to oxygenated blood leaking from damaged capillaries. Within a day or two, the lesion turns a characteristic blue or dark purple as the hemoglobin loses oxygen and begins to break down.
This breakdown continues over the next five to ten days, with the bruise turning greenish and then yellow as the body converts the hemoglobin into the pigments biliverdin and bilirubin for reabsorption. Most simple bruises fade completely within two weeks, though larger or deeper contusions may take up to four weeks to fully resolve. The discoloration changes color and steadily shrinks over this typical timeline, confirming its benign nature as a correctly healing injury.
Understanding the ABCDEs of Melanoma
The established method for self-screening and identifying a suspicious lesion is the ABCDE rule. A stands for Asymmetry, meaning the two halves do not match in shape if a line is drawn through the middle. B represents Border irregularity, where the edges are often notched, scalloped, or poorly defined rather than smooth.
C denotes Color variation, indicating the lesion contains multiple shades (such as black, brown, tan, red, white, or blue) within the same spot. D is for Diameter, as melanomas are typically larger than 6 millimeters (roughly the size of a pencil eraser) when first diagnosed. E is for Evolving, the most significant sign, referring to any change in the spot’s size, shape, color, or elevation over time.
This evolving characteristic is particularly relevant when a lesion mimics a bruise, such as with a subungual melanoma. Unlike a bruise under the nail that will grow out with the nail plate, a cancerous dark streak will remain stationary, often widen, and may show the Hutchinson sign. This sign is pigment extending from the nail bed onto the surrounding skin. Acral Lentiginous Melanoma often presents with these irregular features, lacking the symmetrical, homogenous appearance of a simple bruise.
Signs That Require Immediate Medical Attention
A professional evaluation is necessary for any dark spot that does not follow the predictable healing trajectory of a bruise. If a discolored area persists for longer than three to four weeks without showing any sign of fading, it warrants a visit to a dermatologist. This is especially true for any new dark streak under a fingernail or toenail that appeared without a known traumatic injury.
Immediate attention is also required if a mole or spot begins to change rapidly, especially if it starts to bleed, ooze, become intensely itchy, or feel painful or tender. These symptoms, when paired with the ABCDE characteristics, suggest a change in the lesion’s biological activity that requires a definitive diagnosis. A biopsy is the only way to determine if a suspicious lesion is harmless or a form of skin cancer.