Causes of Dark Patches on Skin

Content provided by the Faculty of the Harvard Medical School

Causes of Dark Patches on Skin

Question:

My skin sometimes gets dark patches, even those areas not exposed to the sun, like my underarms, behind my knees, and inner thighs. It usually happens after an itchy irritation. Sometimes the dark color stays and will not fade. Why does this happen? Is there anything I can do to get the dark area back to its normal color?

Answer:

Skin darkening after irritation is called "post-inflammatory hyperpigmentation." This is a common occurrence and is part of your body's natural healing process. For example, acne bumps are at first pink or red and then change to darker colors before they go away completely. Scratching your skin can cause pink scaly patches that turn brown before going away. Post-inflammatory hyperpigmentation also occurs in areas of friction, where skin rubs against skin, such as under the arms and on the inner thighs.

The dark color may stay for several months before fading. Areas of chronic friction, such as the upper thighs in people who are overweight, may remain pink or brown as long as the irritation continues. The skin will usually return to its normal color if the irritation stops, although fading to the normal color may take many months.

Prevention is the best medicine for post-inflammatory hyperpigmentation, so try to eliminate any skin irritation that starts the process. On small areas, such as acne bumps that have turned brown, bleaching creams can be helpful. These creams should be used only on very limited areas and only as directed by your physician.

Last updated:	May 01, 2009