A rare endocrine disease called Addison’s disease can produce hyperpigmentation that’s most obvious in areas of sun exposure, such as the face, neck, and hands, and areas exposure to friction, such as elbows and knees.
The hyperpigmentation is a direct result of an increased level of a hormone in your body that results in increased melanin synthesis.
Excessive sun exposure can also cause an increase in melanin.
Changes in skin color can result from outside causes.
For example, skin diseases such as acne may leave dark spots after the condition clears.
Other causes of dark spots are injuries to the skin, including some surgeries.
Freckles are small brown spots that can appear anywhere on the body, but are most common on the face and arms. Freckles are an inherited characteristic.Freckles, age spots, and other darkened skin patches can become darker or more pronounced when skin is exposed to the sun.