You've already figured out what's causing this painful problem, Timheat, and sweat. Your skin is wet from sweat, and in time that can exacerbate any irritation caused by clothing or other things rubbing against it. Are you sort of a heavyset guy? Because that can contribute as wellif you're a bit fleshy, then the inside of your thighs can rub together right around the groin area.
The trick is to keep as dry as possible. I'd make it a habit to splash on a drying powder, whether simply baby powder or something a little more exotic such as Gold Bond Medicated Powder (not sure what the Australian equivalent would be if that stuff's not available, but I'm sure a helpful pharmacist can suggest something). You might even use some spray-on anti-perspirant in the area that gives you troublethe active ingredient in that stuff literally shuts off sweat glands.
Next, choose clothing that's good at managing moisture. NO cottonit gets wet and stays wet too long. For the layer closest to the skin I'd recommend a pair of Patagonia's Capilene Lightweight Boxers ($25 in the U.S.; www.patagonia.com). They're very comfortable, and the Capilene material both wicks moisture away from the skin and helps it evaporate quickly. Over that I'd wear any sort of loose-fitting shorts made from light, fast-drying synthetic material. Something like Ex Officio's Amphi shorts ($46; www.exofficio.com) would be fine. Again, you want to wear something that doesn't trap and hold moisture.
So there you go. Hope that solves your irritating problem...
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