Signs of diabetes show up all over the body, from bleeding gums to tingling feet to darkened skin patches on the neck and underarms.

Arsenic is a poisonous metal that has long been linked to an increased risk of cancers, diabetes, thickening of the skin, diseases of the liver and digestive complications.

There's no specific treatment for acanthosis nigricans - but treating any underlying conditions, such as diabetes and obesity, may cause the changes in your skin to fade.