Itchiness of the umbilicus (belly button) can be from rashes of the skin AROUND it, or from an infection within it. Many different rashes can form around the umbilicus, but the most likely one would be a contact dermatitis (allergic-type reaction to a foreign substance on the skin like a cream or a new laundry detergent on the clothes). However, many other skin rashes
can affect this area, and if you have noticed any skin changes (redness, scaliness, swelling), you should definitely make an appointment to see your primary care physician
or a dermatologist.
Another possibility is an infection of the belly button tract. Sometimes, foreign objects such as lint from clothing or body hair can enter the belly button canal and cause an inflammatory reaction. Infections of the canal are often accompanied not only by itching, but a foul odor and/or liquid coming out of the canal. This can be PREVENTED by keeping the area around the belly button clean (washing thoroughly twice daily) and by trimming body hair around the belly button to minimize the chance that it falls off and enters the canal. Infections of the belly button can be TREATED by applying hydrogen peroxide (either by pouring a few drops into the belly button, or by applying it with a q-tip), and removing any foreign objects from the tract. However, especially for the first time, this must be done by a medical professional, so if you have noticed any odor or discharge, I would recommend making an appointment with your primary care physician to take a closer look.