There are few bodily injuries more relatable than bruises. At one time or another, virtually all of us have sustained this injury after bumping an arm or a leg against an object or because we've collided with someone while playing our favorite sport.

But sometimes bruises appear for no obvious reason or without one being able to recall any accident or incident behind it. Some people also bruise more easily than others or seem to experience bruising more often than the rest of us. Hint: A vitamin deficiency could play a role in it.

In such cases, it can be helpful to understand which factors could be behind the bruise and which deficiencies or medical disorders may be contributing to this common discoloration of the skin.

What causes bruises?

Bruises, also called contusions, appear as red, brown, bluish-purple, yellow or black circular blemishes on one's skin. They occur when small blood vessels, known as capillaries, sustain damage and leak their contents just below the surface of the skin.  

While bruises "are usually a result of minor trauma" such as a blow, bump or fall, explains Dr. Cory Fisher, a family medicine physician at Cleveland Clinic in Ohio, several other factors can cause or contribute to them. Zinc deficiency or vitamin B or K deficiencies, for instance, sometimes manifest as bruising. 

More:Zinc is an important nutrient, but get it from food, not supplements, experts say

Bruising can also be a symptom of certain medical conditions or bleeding disorders such as cirrhosis, von Willebrand disease, Cushing's syndrome, or hemophilia. "Bruising is also common in any condition that lowers your platelet count (platelets are responsible for helping the blood to clot) such as blood cancers like leukemia or lymphoma," says Dr. Neha Pathak, chief physician editor at WebMD and a former primary care doctor at the Department of Veterans Affairs. 

"Some medicines can also increase your risk such as being on a blood thinner, steroids, and taking NSAIDs like ibuprofen," she adds. 

Bruises frequently observed on the same individual may also be a sign of physical abuse - something that should be reported to local authorities or to the National Domestic Violence Hotline at 800-799-7233. 

Why do some people bruise more easily than others?

While these conditions, medications or vitamin deficiencies represent several of the reasons some people bruise more often than others, some individuals are more susceptible to bruise for a variety of other reasons. 

One's age can be a major factor. "As we age, our skin gets thinner and at the same time our blood vessels become more fragile," explains Fisher. "This is a bad combination that makes bruising much more common as we get older." 

Genetics and gender factor in as well. "Women tend to bruise more easily than men," notes Dustin Portela, DO, a board-certified dermatologist and founder of Treasure Valley Dermatology in Boise, Idaho. This is likely due to men having about 20% thicker skin than women and because aging women lose significantly more collagen than aging men do, primarily coinciding with menopause. 

Race and body type also play a role in why some people seem to bruise more easily than others. "People with lighter skin tones show bruises more easily and those with more body fat tend to bruise easier," says Dr. Steven Maher, an emergency medicine physician at Mayo Clinic in Arizona.

How long do bruises last?

Though various causes like these result in some bruises lasting longer than others, "generally, bruises last about one to two weeks," says Portela. "Before fading away, they go through color changes as they heal, from red/purple to yellow/green."

Among the factors that determine how long bruises last are how serious the cause behind the bruise is and where the bruise is located. "Bruises on the legs and arms are very common," says Fisher, "and if the bleeding is significant enough, a large collection of blood can form - which is referred to as a hematoma."

If you'd like to accelerate healing time, "try applying a cold compress immediately after an injury, elevate the area, if possible, and later switch to warm compresses to increase blood flow," advises Pathak. "But there's no instant cure for bruises - time is the best healer."