How to convince my brother to take his shirt off during summer?

We've been suffering a spectacular heatwave in this part of the world. We live in a South American country where springs, summers and autumns are really muggy, it's cold only during winter. The problem is that temperatures have been above 113F and my brother doesn't want to take his shirt off not even for sleeptime. He says that he doesn't like his body. He often gets really sweaty during afternoon, but even my daddy offers my bro to pull his shirt off but he doesn't want. My bro chose another ways to deal with heatwave.