I have been taking Cephalexin 500 mg for a sinus/throaght infection that I had, on the 9th day, I discovered a had a rash on my arms, uper legs, chest area. I have now finished with the medication, and the rash seams to be getting somewhat better. I have been taking liquid Bendyle and rubbing cortizone & anti itch creams on the areas. Do I need to be concerned, I am watching it, and as I said it appears to be improving. At first I didn't associate it with the antiboitics, but then I started researching about it on the net and have discovered that it it a side effect.. That is the only side effects I have experienced, along with a little diarrea, but not severe. I have not contacted my doctor, because I wasn't sure if it was a problem.