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It’s very rare to have spontaneous bruising without any reason. People who are prone to bruising may not remember a minor trauma and assume that the bruise has appeared out of nowhere. Most bruising occurs as a result of some kind of injury.
Dr. John Cunha on eMedicineHealth explains that discoloration on the skin is caused by tiny blood vessels breaking under the skin. This causes blood from damaged veins and capillaries to collect near the surface of the skin. A bruise usually starts off as a black and blue patch of skin and gradually turns green or yellow as it heals.1
You may find that the bruises on your body are painful at first but they may start to itch as they heal. Dr. Cunha says that it will take between one to two weeks for bruises to completely heal.2
Causes of Random or Unexplained Bruising on your Body and Legs
Knowing the reason for the appearance of mysterious bruises can help to prevent them in the future. This can also help you to determine if you should see a doctor about unexplained bruises that have appeared on your body.
Aging
Older people tend to bruise easily because of changes to their skin as they age. Doctors from the Mayo Clinic explain that aging causes the protective fatty layer in the skin to become thinner. This means that elderly people are more prone to random bruising than younger adults.3
According to a report prepared by the University of California, elderly people may also be less stable on their feet and can bump into objects frequently causing accidental bruising. However, the report recommends that any unexplained bruising on an older person be investigated to rule out the possibly of abuse. Authors of the report said that 90% of bruising occurs on the legs and arms and very rarely on the neck, ears, buttocks, or soles of the feet.4
Vitamin deficiency
One cause of random bruising on legs or bruises that appear after a minor injury is a vitamin deficiency. For example, a lack of vitamin C can lead to scurvy which causes unexplained bruising and bleeding. Vitamin K is needed to help blood clot properly and prevent random bruising.
The Journal of the American Academy of Dermatology reported that ascorbic acid (vitamin C) helps to strengthen blood vessels and prevent them breaking. Vitamin C supplements are also used to help reduce random bruising in patients suffering from skin diseases that cause bruising.5
According to MedlinePlus, vitamin K plays a major role in blood clotting. Vitamin K supplements are often given to prevent unexplained bruising in people who take blood thinning medication.6