Good Morning Netters,] A good friend of mine that is an urologist explained to me what happens with acidic urine. Due to dehydration, or a metabolic problem, the pH of urine drops and becomes acidic. From there uric acid crystals form and the precipitation causes the red, "brick dust" looking urine, or spots on the diaper. If it continues, yes it is harmful. It alerts the system that something is wrong. That is why children or adults that display those symptoms will be given IV's or something to alkalize the urine. In the case of infants, with an increased milk (hopefully breast milk) intake the "brick dust" disappears. I have been told also over and over again that it is not harmful, but one does need to take action to assure adequate intake. Have a good day all. Pat Bull, RN, IBCLC The Breastfeeding Connection/Medela, Inc. Naperville, IL