Hemosiderin — a protein that stores iron in the body — can accumulate under the skin and in major organs. As a result, you may notice yellow, brown, or black staining or bruising. Stains most often appear on the lower leg, sometimes covering the space between your knee and ankle.

This happens because of hemoglobin, a protein molecule that contains iron. The hemoglobin in your red blood cells is responsible for carrying oxygen from your lungs to other tissues. When red blood cells die, the hemoglobin releases iron. The iron is then converted into hemosiderin and can be stored in your tissues beneath the skin, causing hemosiderin staining.

Hemosiderin staining occurs when red blood cells die, causing hemoglobin to trigger hemosiderin production. Your body’s white blood cells, or immune system cells, can clear up the excess iron and hemosiderin released into the skin. But there are some medical conditions that can prevent this process, resulting in a stain.

Some common causes of hemosiderin staining include:

If your hemosiderin staining occurred as a side effect of laser treatments, it will likely clear up on its own. Staining due to slow-healing health conditions or wounds may never go away. The marks may lighten over time, but not in all cases.

Hemosiderin staining is more than an eye sore. This bruising can be an indication of poor blood circulation and can trigger chronic pain and other serious conditions.

Damage to blood vessels can cause surrounding tissues to flood with blood and affect blood flow to the body. As a result, you may develop medical conditions including:

Hemosiderin can also accumulate in organs, such as the liver and lungs. Staining in the liver can indicate hemochromatosis, or an iron overload. Left untreated, this condition can lead to a number of medical complications including:

Excessive hemosiderin and staining can also affect brain function. While more research is needed to confirm findings, researchers have potentially linked hemosiderin staining to chronic brain disorders including:

There are treatments available to lighten or reduce staining. Topical creams and gels are common forms of treatment. These topical treatments can help prevent hemosiderin stains from darkening over time, but in some cases may not remove the entire bruise.

Laser treatments have also begun to evolve as an effective treatment for hemosiderin staining. You may need to be treated in more than one session depending on how dark the stains are and where they are located. Similar to topical ointments, laser treatments are not guaranteed to remove the entire stain. It may significantly improve the cosmetic appearance, though.

In milder cases of hemosiderin staining, the bruising may sometimes vanish on its own or lighten over time. Discuss your treatment options with a doctor.

Hemosiderin staining produces bruise-like marks on your body that can range in color from yellow to brown or black. Though it can appear anywhere on the body, it’s more prevalent on the lower legs. In many cases, hemosiderin staining can be permanent.

The staining alone isn’t life-threatening, but it can be an indication of a more serious condition. If you notice discolored marks on your body or experience irregular symptoms, schedule a visit with your doctor to discuss treatment.