Hi, my 2 1/2 year old recently had a bed cold out which she came out with a rash..its mostly underneath her knickers(100% cotton except elastic).I thought that it was elastic but when I put a pair with elastoc hemed in she still got a rash.So I guess it must be detergent. What now, what to use? (been using Arial biological gel)Thou why its limited to her knicker area its anybodys guess..