I noticed some comments about the smell of synthetics. Nylon is a synthetic but very resistant to smelling. Yes, you can make it smell if you jam it right against your underarms, but then cotten will also stink in these conditions and wool too for that matter.
I am not exactly sure of why polypropylene and polyester stink so quickly, but I do understand why they keep on stinking even after washing. Namely, because they don't absorb water. Body oils can get pressed into the fibers, but then it is very difficult to get these oils out, because of how the fibers don't absorb water.
By contrast, nylon absorbs just enough water to make it very easy to clean, but not nearly so much as cotton and wool (for comparable strength garments) and thus it dries quickly.
I have several times worn my supplex nylon shirts for a week at a time without washing them, while hiking in desert-like conditions (100°F heat and sunny). The shirts start out light grey and by the end of the week are coated with white streaks of salt, but they don't have any smell, provided I keep them away from my underarms (which is possible if I use the Jardine one shoulder carrying method). Beyond a week, the shirts will start to smell due to body oils going rancid. These salt-stained shirts can then be washed very easily in cold water in a sink, and they come out perfectly clean.
The real secret to comfort in desert conditions, regardless of the fiber, is to allow ventilation. So buy a shirt of either supplex/taslan or cotton or polyester/rayon--it really doesn't matter which--but make sure it fits very large so you get plenty of airflow. Long sleeves will help protect the hands. The Jardine one-shoulder carrying method allows maximum ventilation. Carrying the pack with both shoulders and a hip belt results in minimum ventilation.