Dark spots on the body indicate a case of liver spots, which are also called age spots, because the condition is related to skin being unable to repair itself after being exposed to ultraviolet light.
Ultraviolet light comes in two bands of radiation. UVA is the first band of radiation that causes the well-known skin tanning that occurs when you step out into the sun. UVB radiation is another band of radiation that also causes tanning but causes the tan to appear much slower and the tan becomes more permanent. The permanent nature of the tan is because the skin responds to the exposure to UV radiation by increasing the amount of skin pigment called melanin in the area – a process called melanogenesis. Melanin is not just a skin pigment. It is the natural form of sunscreen that filters UV radiation as it hits the skin and converts it into heat. Over time, melanin in the skin becomes darker because of the oxidative effect of ultra violet radiation. This process of conversion of UV radiation to heat is however not perfect and UV radiation can still get through into the skin due to prolonged exposure to the sun for a long enough period. Once this happens, cellular damage to the skin occurs and this has to be repaired. With countless exposures to the sun in this way, the skin eventually loses the ability to repair itself and a collection of melanin is then created to form a brown blemish on the surface of the skin called a liver spot or an age spot. With more exposure, the brown turns into black and therefore the dark, hyperpigmentation spot on your face.
Once you have an age spot, you have to realize that your skin is getting too much exposure to the sun and that you have to start limiting the exposure permanently or start wearing sunscreen whenever you step out. Sunscreens with the highest SPF levels should be worn and reapplied whenever possible. SPF levels indicate the level of protection time that you have before you have to step back indoors. Therefore, an SPF level of one would indicate the normal time you can spend in the sun without getting a tan and three would indicate thrice that amount of time. The same applies to levels like 40 and 50. Try and also increase the level of antioxidants in your body by consuming more vitamin C and E that are rich sources of it. These reduce the cellular damage to your skin caused by free radicals.