It Could be hyperpigmentation. General advice is to use sunscreen ALL OVER YOUR BODY not just face (SPF 30+). Anecdotally, Kojic Soap os recommended by many but for safe lightening. There arent real risks with Kojic like other lightening methods like mercury or hydroquinon, so i think it trying wont to hurt. This is general advice only. Going to a DERMATOLOGIST (NOT just a general doctor) is important if the situation does not improve. Don't assume that just because your body is covered by clothes that it is protected from the sun. UV light penetrates clothes like water or ሻይ penetrates ማጥለያ። Wear sunscreen 👍