A bruise, medically known as an ecchymosis or contusion, is a common occurrence resulting from an injury to the body. While it might seem like bruises “spread” or change in size, this appearance is actually a part of the body’s natural healing process. Understanding the biology behind a bruise reveals why these marks on the skin evolve in both color and apparent dimension over time.
What a Bruise Is
A bruise forms when small blood vessels, called capillaries, beneath the skin are damaged by an impact or injury. This trauma causes these tiny vessels to rupture, allowing blood to leak into the surrounding tissues. Since the skin remains unbroken, the blood pools just below the surface, forming a visible mark.
The pooling of blood under the skin is often referred to as a hematoma, which is essentially a localized collection of blood outside of blood vessels. The initial appearance of a bruise can vary, often starting as a red or purplish mark, which may also be tender to the touch. The body’s blood cells, specifically platelets, begin to work on repairing the damaged vessels to stop the bleeding.
Why Bruises Appear to Change
Bruises do not truly “spread” like an infection, but leaked blood can seep into adjacent tissues and move downwards due to gravity, making the bruise appear larger or shift location over time. The change in a bruise’s appearance, including its evolving colors, reflects the body’s process of breaking down and reabsorbing the pooled blood.
The color changes occur as the iron-rich hemoglobin in the trapped blood breaks down. Initially, a bruise may appear red because of fresh, oxygen-rich blood. Within one to two days, as the blood loses oxygen, the bruise turns blue, purple, or even black. After about five to ten days, the body converts hemoglobin into compounds like biliverdin and bilirubin, causing the bruise to appear green or yellow. Finally, around 10 to 14 days, the bruise becomes yellowish-brown or light brown before fading completely as the body reabsorbs the remaining pigments.
Factors Affecting Bruise Characteristics
Several factors influence how a bruise looks, how long it lasts, and how quickly it heals. Older individuals bruise more easily because their skin thins and loses some of its protective fatty layer, which cushions blood vessels. Blood-thinning medications, such as aspirin or warfarin, can increase the likelihood and severity of bruising by impairing the blood’s clotting ability. Corticosteroids also contribute to easier bruising by thinning the skin.
Skin tone affects how bruises appear; on darker skin tones, bruises initially look darker brown or black with less noticeable color changes compared to lighter skin tones. The bruise’s location also plays a role, with areas having thinner skin or more blood flow bruising more visibly or healing differently. The severity of the initial impact directly relates to the bruise’s size and intensity, as harder blows cause larger bruises. Deficiencies in certain vitamins, like C or K, also make a person more prone to bruising.
When to Seek Medical Advice
While most bruises are harmless and resolve on their own, certain characteristics warrant medical attention. Consult a healthcare provider if a bruise is very large or extremely painful, or if it appears without any apparent injury. Bruising around the head or eyes, especially if accompanied by vision problems, also requires evaluation.
Seek medical advice if a bruise does not show signs of improvement after two weeks or worsens over time. Other concerning symptoms include persistent swelling, a lump forming in the bruised area, or unusual bleeding elsewhere in the body, such as nosebleeds or blood in urine or stool. Unexplained bruising, particularly if frequent or occurring in unusual locations like the abdomen or trunk, may indicate an underlying medical condition.