The most common cause of brown skin spots is sun damage, but the spots can also a be symptom of Addison's disease, a condition that causes decreased adrenal gland hormones, explains Healthgrades. Brown spots that are naturally present at birth are referred to as cafe au lait macules.
Brown spots on the skin can also be a symptom of melasma, a skin condition that causes brown patches on the chin, cheeks, chin and forehead, explains the American Academy of Dermatology. While the specific cause of the melasma is not completely understood, it is believed to be triggered by hormonal fluctuations caused by pregnancy or birth control pills, adverse reactions to cosmetics and sun exposure, adds the American Academy of Dermatology.
In certain cases, brown spots on the skin can be a sign of skin cancer, so it is important for individuals with unexplained brown spots to consult with a dermatologist, explains the Skin Cancer Foundation. Additional potential signs of skin cancer include spots, moles or birthmarks that crust over or bleed; brown skin spots or patches with irregular borders; and spots or freckles with unusual textures. Ultraviolet radiation is associated with approximately 90 percent of all non-melanoma skin cancers, so it is imperative for individuals to take appropriate safety measures, such as applying sunscreen and wearing protective clothing and eyewear, while in the sun.