On the average person, a black bruise is most likely the result of some type of injury. Certain diseases such as hemophilia, leukemia, or lymphoma may also result in black bruising. Some people also tend to bruise more easily than others as a result of a variety of factors not related to disease. Nutritional deficiencies, certain medications, and the age of a person also have an effect on how likely they are to develop any type of bruise.
In most cases, a bruise that is black has been on the body for at least a few days. Bruises go through many colors as they heal, and tend to look much worse before they look better. Green, purple, blue and black are the most common bruise colors. If a black bruise was the result of an injury, it may also swell up slightly and feel tender to the touch. People who bruise easily often become concerned because they may not recall what happened to cause the bruise.
A black bruise on someone with hemophilia is usually the result of bleeding underneath the skin. People with hemophilia bleed more freely than others because they do not have enough clotting agents in their blood to make it stop. This can cause excessive bruising on the body from very minor accidents. Most hemophiliacs are diagnosed with the disorder around the age of one or two, which is when most babies become active and start developing bruises as a result of increased play.
Leukemia and lymphoma are other diseases that may result in excessive bruising. Both diseases are forms of blood cancers and result in a lower platelet count in persons affected. People who have either disease may notice a black bruise or bruises on their bodies. Their bruises are typically a result of minor injuries or accidents that are likely not memorable and wouldn't cause a bruise under normal circumstances.
Not everyone who notices many bruises on their body is likely to have a disease. Sometimes people bruise easily because they are anemic, have low levels of iron in the blood, or are deficient in certain types of vitamins. Women are normally more prone to bruising than men, and most people notice more bruises as they age due to thinning of the skin. Additionally, people taking blood thinners or other prescription medications bruise frequently as a result of the drugs. A person who is concerned by a black bruise or any amount of excessive bruising on the body may be able to ease their worries by speaking with a doctor to rule out any serious causes.