Darkened skin---known as hyperpigmentation---can be an indicator of certain conditions. According to the New York Times, hyperpigmentation arising from medical conditions is sometimes mistaken for sun tan, although the causes and onset are different. Typically hyperpigmentation that occurs as a result of a medical condition may start in a small area like the elbows, and then extend to larger areas of skin as the condition progresses.
Medications and Metals
According to American Family Physicians, many medications can cause hyperpigmentation. This happens in one of two ways: either the skin darkening is a direct side effect of the medication or the medications cause a phototoxic reaction that causes the skin to abnormally darken with sun exposure. For instance, some antibiotics may cause phototoxic reactions while certain oral contraceptives may cause hyperpigmentation. Ingestion of certain metals may also cause skin discoloration that presents as hyperpigmentation, as well, including colloidal silver, gold and mercury.
Chronic Sun Exposure
American Family Physicians also cites chronic sun exposure as a common cause of hyperpigmented lesions. This is different than a sun tan, which is caused by a temporary increase in melanin production following short-term sun exposure. Lesions resulting from chronic sun exposure, on the other hand, usually occur as permanent dark spots like freckles or age spots. This type of skin darkening is easily avoided through the consistent use of sunscreen or avoidance of UV radiation.
Addison's Disease and Other Endocrine Disorders
According to Merck, Addison's disease is a progressive illness caused by underactive adrenal cortex function. It is most likely an autoimmune disease, but it can also be caused by adrenal tumor and other conditions. The disease can exist as a stand alone disease, or it can be secondary to another illness. Hyperpigmentation from Addison's Disease often starts as a tanning or bronzing on bony parts of the body like the knees or knuckles before it extends to other areas of the skin. Other disorders of the endocrine system may cause similar hyperpigmentation.
Rosacea
Rosacea is a condition that causes a reddish darkening of facial skin. According to the National Rosacea Society, the disorder affects more than 16 million Americans. In spite of these numbers, it still isn't well understood by medical science. The cause remains unknown; however, there are medical treatments available that can help to minimize the signs and control the symptoms of rosacea.
References
- New York Times Health Guide: Skin---Abnormally Dark or Light
- AAFP American Family Physician: Common Hyperpigmentation Disorders in Adults: Part I. Diagnostic Approach, Caféau Lait Macules, Diffuse Hyperpigmentation, Sun Exposure, and Phototoxic Reactions; Daniel Stulberg M.D., Nicole Clark M.D., Daniel Tovey M.D.
- : Merck Manuals Online Medical Library: Addison's Disease
- National Rosacea Society: What Is Rosacea
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