Diaper rash is an inflammation that develops in the diaper-covered area. The medical term for this condition is "Irritant Diaper Dermatitis". It causes mild redness and scaling on your baby's bottom, and at times, you'll see an outbreak of spots that resembles heat rashes. The inflammation causes itch and pain, and if the condition worsens, the skin may become sore and may bleed. The rash may spread outside the diaper area onto the waist or thighs. Skin inflammation around the thighs where the diaper gathers are in direct contact with the baby's skin are also diaper rashes.