Hello. I am a 39 yrs male. The skin in the middle upper/outer part on my left thumb has darkened since a month (area of around 1 inch). Often, it itches and becomes reddish black. At that time it seems as something is going on below the skin too! After a day or two the itching and other issues subside and the skin remains blackish. This keeps on continuing. Since some days skin is being shed from the region in small white patches. I consulted a general physician and he said its due to allergy. But I had no recent change in food habit or anything that might have triggered an allergic reaction. Whats this problem? What should I do?