Freckles are small and flat light brown spots most commonly found on sun-exposed surfaces. Most commonly, poor pigmentation is the reason. Very fair and red-headed people are more likely to have these. They are harmless and most fade away in winter. Some peculiar appearing freckles may become skin cancer.
Freckles appear due to an increase in the dark pigment called melanin and an increase in the melanocytes. Certain people with a genetic predisposition may be more prone to it as well as sun exposure can be a reason too. A freckle is nothing but an extra deposit of melanin at one spot of the skin.