As Baby grows and begins to achieve milestones, so goes the process of trial and error with things like foods, drinks and medicines. While most things not tolerated well by the digestive system are apparent through quick or immediate reactions, some reactions take a bit of time to show up. Sometimes a reaction shows up in the form of a painful, uncomfortable diaper rash.
Be tender with the area. Use either chemical-free or sensitive wipes, and blot instead of wiping as much as possible. Try giving Baby a warm saltwater soak in a tub or the bathroom sink. If you have a saltwater pool and weather permits, this may help as well. Best thing is to air dry as much as possible, as messy as it may prove to be. Plastic diapers meant to hold in wetness can be more of a hindrance when you're trying to keep Baby's skin dry. Maybe keep a few cloth diapers on-hand, and wash them in the gentlest detergents possible to minimize irritation.
For more severe cases, contact your doctor for further advice on what products to use. The doctor may ask to see the child to determine the severity and cause of the rash. For yeast infections, your doctor may prescribe or suggest an OTC anti-fungal to mix in with a diaper cream with a high concentration of Zinc Oxide. When you find a product that seems to work well and quickly for you, be sure to take note and stock up for future incidents!