Hello. Thank you for writing to us at healthcaremagic This is most likely a result of Allergic Contact Dermatitis (ACD) most likely to nickel which is commonly present in the buckle of belt or the button of his jeans. The location of the spot is exactly the same place where a belt buckle or jeans button would come in contact with his abdominal skin. This goes in favor of ACD. Contact Dermatitis such as this can be treated with a mid potent topical steroid e.g Mometasone furoate 0.1% to be applied, twice daily. Another possibility if that it could be a tinea/fungal infection. Tinea is very common at the waist line. I would suggest a KOH preparation made from the scarping and scanning under the microscope to look for fungal elements. If fungal elements are seen it should be treated with a topical antifungal e.g either Clotrimazole 1% cream Or Miconazole 2% cream, twice daily. I will suggest that you visit a dermatologist for a confirmatory diagnosis as well as appropriate prescription. Regards