Dr. Greene's Answer
Parents are often concerned when they find crystals in the diaper. By far the most common cause of these crystals is urate–something normally found in urine. And when the concentration is high, crystals form. They can be hard, but they are most often soft, like tiny cubes of Jell-O. They can be pale or clear, but often have an orange tinge, leading many parents to be concerned about blood.
Urate crystals are more common when kids are dehydrated, but are also common in healthy, well-fed babies. The inner lining of the diapers can also contain moisture-absorbing crystals that sometimes leak out if there is a little tear in the diaper. Urate crystals are not painful to babies. If your pediatrician suspects these are a different type of crystal, the material can be tested at the lab. Urate crystals are most common in the first few months of life.