Hi! I think you're describing fungal infection (like tinea versicolor) na commonly nakikita sa back, ang green-ish o dark patches na kumakalat? Kailangan talaga ng doctor para ma-diagnose properly at ma-prescribe ang tamang antifungal, kasi kung hindi tamang gamot, mas lalaki lang or magiging stubborn pa. A few of us mums had similar concerns with our kids, at ang dermatologist ang nag-confirm at nag-give ng specific cream or oral medicine depending sa severity. Especially kung umaakyat na siya sa likod, mas better na makita ng doctor agad para ma-stop agad before it spreads further!