How does it feel to suddenly sprout a few bruises or go home with a few? You would have a tough time explaining the cause especially since you did not know it existed in the first place. It might be mild discolorations and even black or blue marks normally associated with blunt trauma injuries.Though generally harmless, such bruises may be a cause for concern and if you detect one that persists or grows or multiplies, consider taking medical help.
The reasons for such non-injury bruises are various. It could be the result of prolonged exposure to the sun, vitamin deficiency or even a serious hidden medical condition.

Blood Disorders
Some people bruise too easily due to some disorders. Unexplained bruising can be caused by the breaking of small capillaries under the skin. This causes blood to leak into the surrounding tissue causing discoloration and bruises. Leukemia, which is cancer of blood-forming tissues, hemophilia, factor X deficiency and acquired platelet function disorder are some of the reasons.
Medicinal Causes
 
Bruising can be caused by an adverse reaction tomedicines. If there are no obvious reasons for bruising, medicines may be the reason. Aspirin and clopidogrelused to prevent heart attack and strokes can cause bruising. So can non-steroid anti-inflammatory drugs,anti-coagulants and antiplatelet medicines. Medicines that contain corticosteroids taken internally or applied to the skin can also cause bruises in some cases.
Nutrient Deficiency
Vitamins are vital for the body. They help to maintain the level of minerals in the body and also the formation of red blood cells. Vitamin C also lowers cholesterol. It quickens the pace at which wounds heal and boosts your immune system. Lack of Vitamin C may cause bruising. Iron keeps your blood cells healthy and its deficiency may cause you to bruise easily. Vitamin K deficiency slows down the rate at which blood clots causing it to collect under the skin and form bruises. Vitamin B12 deficiency can make the blood vessels very fragile causing bruises. Eat fatty fish, nuts and bananas to restore Vitamin K. Vitamin B12 can be restored with fish and lettuce. For Vitamin P, consume apples, garlic and pumpkins. Vitamin P can also help in producing more collagen.

Diabetes

Diabetes affects the ability of your body to produce and use insulin. It slows the pace of your healing and allows bruises to stay
Hormonal Imbalance
Hormonal imbalance is a medical condition which affects the endocrine system causing disruption in the levels of various hormones in the body. Too much of estrogen weakens the cell membrane. Lack of progesterone, on the other hand, causes bruising and so it is necessary to maintain adequate levels.
Changes Related To Age
With each passing year, signs of bruising on the skin become more frequent. The skin loses the fatty layer that protects the blood vessels from injury. The capillaries, which are tiny blood vessels located within the tissues of the body, near the skin surface can break with an impact from even a mild injury.
There may be numerous other causes which lead to unexplained bruises on our body like genetic disorders that prevent the blood from clotting. When such bleeding leads to blood getting trapped under the skin, it forms a bruise. Most instances of random unexplained bruising are nothing to worry about. They usually go away on their own. Home remedies like an ice pack to reduce blood leakage into surrounding tissues or heat to increase blood circulation can prove effective.
But if it persists and spreads in size or numbers, it is time to consult the doctor.