The reasons for the appearance of brown spots in the leg?

Multiple: Brown spots on the skin of the leg can develop from several sources. The most common is a sun spot which originates from sun exposure. These are also called lentigos. You could also have a newly developed nevus or mole which can develop throughout your life and not be abnormal. Pre-cancers and cancers can appear as brown spots, as well, and should be evaluated by a skin doctor.

Many possible causes: Brown spot could be freckles , lentigines, nevi or many other possible causes . [ including bruises , hyperpigmented or scarred areas] . It would be best to have the legs examined by a doctors to find out. Some of the brown spots may need medical treatment.