A 36 years old factory worker developed itchy annular scaly plaques in both groins. Application of a caicosteroid ointment led to temporarY relief but the plaques continued to extend at the periphery. The most likely diagnosis is -

Itchy annular lesion in groins with scaling and peripheral spreading and central clearing indicates tinea cruris initially tinea responds to coicosteroids due to masking of infection by steroid effect. iadvl textbook of dermatology, page page 253