goodtoknow says: Nappy rash causes a red, blotchy rash making your baby's bottom look very sore. But it's usually mild and easy to treat. The best thing you can do is keep your baby's nappy off for as long as possible. Change the nappy regularly and wash the nappy area with plain water. Nappy rash is often caused by contact with the chemicals in urine and faeces but can also be due to an infection with the germ Candida. This is sometimes called nappy thrush and can be treated with anti fungal creams.
For a full medical explanation of the causes, symptoms and treatments of nappy rash from patient.co.uk, read on.
Most babies develop a nappy rash at some stage. Usually it is mild and does not bother the baby. It can usually be cleared with the measures detailed below.