Round, expanding spots on the thighs that increase in number are most commonly due to a fungal infection (ringworm/tinea), and the lack of improvement with Dexoderm is expected because it contains a steroid, which can actually worsen fungal infections and make them spread. The correct treatment is to stop using steroid-containing creams and start a proper antifungal cream (such as clotrimazole, ketoconazole, or terbinafine) applied regularly for at least 2-4 weeks, even after the spots start improving. Keep the area clean and dry, avoid tight clothing, do not share towels, and wash clothes in hot water to prevent the spread. In more extensive or stubborn cases, a doctor may prescribe oral antifungal medicines. If the rash continues to spread or does not improve within 2 weeks of correct treatment, it is important to consult a doctor for confirmation and stronger therapy.