Why do Bruises Itch?

Why do Bruises Itch?

Bruises, known medically as hematomas, form when blunt trauma occurs somewhere on an individual’s body. This trauma causes small blood vessels located under the skin, to break. Blood escapes from these broken vessels and seeps into the surrounding tissue. Once in the soft tissue, red blood cells break and the protein hemoglobin leaks out. Hemoglobin is the protein in blood that gives it a red appearance. This is why bruises will appear red in color when they are new. As they heal, bruises will lighten in color slowly, but they may also cause pain or itch. There is no definitive answer for why bruises itch, but there are several theories.ⁱ

1. Bilirubin

One theory suggests that itching of a bruise may stem from an accumulation of bilirubin in the bruise during the healing process. While doctors do not understand why, when high levels of bilirubin are found in the blood, itching is common.ⁱⁱ Elevated bilirubin levels are caused by the release of enzymes by the liver or during the breakdown of red blood cells, as is the case when any blunt force trauma causes a bruise to develop. For this reason, bruising can be common in many illnesses that affect the red blood cells, such as sickle cell anemia, lupus, leukemia and lymphoma. Frequent bruising is also common in conditions that affect the liver, bile duct and gallbladder, such as cirrhosis, hepatitis, Gilbert syndrome, Dubin-Johnson syndrome, cholestasis and tumors or gallstones. All of these conditions typically result in heavy bruising that itches in many cases.ⁱⁱⁱ Jaundice is another condition that causes elevated bilirubin levels and is common when there is damage to the liver. However, with these more serious conditions, there is also a tendency for the bilirubin to accumulate under the skin in general, rather than in an acute location, such as what is experienced when a bruise occurs. When intense generalized itching occurs all over one’s body, it is a condition called pruritus. ^iv

2. To facilitate circulation

Another theory as to why bruises may itch is that it may facilitate circulation to the damaged area. When a wound such as a bruise heals, there are many processes occurring simultaneously to facilitate healing, including the addition of nutrients, the removal of waste products, enhancement of the structural integrity, the renewal of cells and even apoptosis (death of cells). These processes all rely on robust blood circulation and itching provides a way to promote enhanced circulation that will ultimately lead to a more efficient wound healing process.^v

3. Stimulation of nerves

It is also thought that perhaps the cause of itching during the occurrence of a bruise is due to the increased stimulation of small sensory nerves in the area of the trauma. These nerves are stimulated by the blood, plasma, collagen and other substances present during the healing process of the traumatized nerve endings.^vi This is an interesting idea because in regard to the sensation of itching, this is the least understood sensation in regard to the cellular and molecular mechanisms resulting in the itch. The underlying neural circuits are still in the process of being identified. Despite this, researchers acknowledge that any lesions in the peripheral nervous system or central nervous system are capable of resulting in itching.^vii

4. The presence of histamines

Another common theory as to why bruises itch is the presence of histamines during the bruising and healing process. Such as with liver disease, any condition that causes an abundance of histamines to be found in the blood stream can cause unexplained bruising. Bruising itself also may increase histamine levels. This happens when a bruise causes inflammation of the traumatized area. This inflammation releases histamines in the area, which then cause itching.^viii The inflammation may also be a result of the white blood cells arriving to prepare for fighting an infection (common during trauma wounds). The signs of inflammation are redness, swelling and warmth.^ix The release of histamines during inflammation is the reason why itching is a common side effect of an allergic reaction since that is another instance in which high levels of histamines are found.^x

5. From contraction, due to healing

It is also thought that when a bruise, which is essentially a type of wound, heals it also contracts and the process of contracting can result in itching.^xi This theory is based upon recent research indicating that there are itch-specific nerve cells in the skin (previously, it was thought that pain nerves also transmitted the sensation of itching). During the third stage of healing, which is called the proliferation stage, a wound heals and closes by putting cells that flow downward to the base of the wound where they unite with other cells that ultimately pull together to close the wound. The contraction that occurs as the wounds is pulled closed stimulates the sensation of itchiness.^xii