Rash from Bike Shorts

[bellissima]

I started seriously riding this summer. The problem I'm having is that the last two times I've gotten off the bike after longer rides, I have a terrible rash on my thighs right where the bike shorts start above the knee, going up my thigh about six inches. It is not at all itchy, but red, raised and blotchy. Does anyone have any idea what's causing this? Thanks

If your Shorts have silicone leg grippers that is most likely the cause.