For a longer term solution, assess your baby's diet to see if there are any identifiable culprits. Add a probiotic or incorporate lots of organic, plain yoghurt to baby's diet which will help balance the intestinal flora. Do this especially if your child is taking antibiotics as they tend to deplete the stomach of both the good and the bad bacteria.
Another culprit for frequent/persistent diaper rash is Candida, the fungus that causes a yeast infection. If baby's bottom is bright red and shiny and has raised blotches, yeast may be the reason. All the above tips will help, especially the probiotics, but here are some additional remedies you can try for yeast if you want to avoid giving your child anti fungal medication:
Tea Tree Oil (external use ONLY): put a drop of tea tree essential oil into a heaped tablespoon of almond oil and either add to your baby's bath or massage onto baby's bottom. Make sure you dilute it as it will sting if you don't!
Yoghurt: we talked about incorporating probiotics into your child's diet but smearing plain yoghurt directly onto the diaper area is also great for yeast infections! The coolness of the yoghurt will help soothe the inflammation and you'll be kung fu(ngus) fighting the germs too. Double whammy!
GSE: one of my all time favourites and safe to use, even with a newborn! You can make a wash by adding 5 or so drops of it into a jug of warm water and applying to the rash or as an oral dose by mixing 1-2 drops with some juice. If you're breast feeding, take it yourself and it will move downstream to your child (adjust the dose accordingly).
Change detergent/diaper brand: if you are not using a natural laundry detergent, this may be the time to make a switch. I noticed R's eczema changing for the better the moment I switched from a regular (hypo-allergenic mind you) detergent to one free of harsh chemicals. Same goes for your brand of diaper.
Here's to soft skin, as smooth as a baby's *rash free* bottom!!