When I go out in the summer, people are always asking me if I'm hot under all that clothing, but actually, I find that it cools me down.
If you wear light, loose clothing, then it won't cause you to feel any hotter, and it should protect you from getting heated from the sun directly contacting your skin.
Usually, when you hear hot weather alerts, they'll warn people to wear long-sleeved clothing, because it protects your skin from getting burned.
Have you ever gotten sun-burned while covering your skin?
Guys are not required to cover their heads, but the men in the Middle East often do. And they live in the hottest place on Earth; I'm pretty sure they wouldn't do that if it made them feel hot.
Obviously if you're wearing something like wool or leather then you're going to feel hot, but try just wearing a loose, light, cotton long-sleeved shirt.
And long skirts make you feel hot? What kinda skirts are you wearing, cuz I feel a lot cooler wearing a long flowy skirt than wearing jeans.
To keep cool in the summer, I suggest buying some light scarves from an islamic store. Usually the ones you find in the accessories section of a store at the mall are silk or satin, which feel uncomfortable in the heat (for me, at least), but the ones at islamic stores are usually light and comfortable. Those ones can actually make you cool down in the heat.
For clothes, just get a light shirt from a store. If you're concerned about a light shirt clinging to your body, just get it a size or two larger than yours.
I feel comfortable wearing jeans in summer, but long skirts would prolly be more comfortable in the heat.
Hope that helps =]
