I get this too. I actually got a blister welt on one leg with lots of red dots further up. They weren't itchy but sore and hot to touch. So I am not sure if it's an allergy to the gripper (which is silicone)

I suspect it was a combination of heat, sweat and the grippers rubbing on my skin to form the blisters but I don't know what causes the red raised dots further up my legs.