It's often best to treat the cause rather than the symptom. There are a number of options that could be causing the rash. It may take some troubleshooting...

Options:
1. Some kids can develop a suede intolerance. What is the wicking fabric in your nappies, suede or mircrofiber or fleece? Trying a liner, or switching to microfiber lined or fitted nappies might help to see if it could be the fabric. It's not common but does happen.

2. Thrush - Redness will reoccur after every poo. Try a probiotic, either for you if you're BFing or in their formula. You might need to go to the chemist to get an anti-fungal cream to use on the bottom instead. If it is thrush, it is important to treat the source, which is the gut, rather than just the visible symptom of the bottom rash.

3. Wee/Poo is too acidic - if you are BFing check your diet to see if you are eating things that might be too acidic like orange juice, peanuts, that sort of thing.

4. Wee/Poo is too alkaline - happens during teething due to excess saliva. If you're BFing take an acidic vitamin C.

5. Are you using cloth wipes or store bought? Store bought often have anti-freeze as their preservative which can irritate the skin. A wash cloth, cloth wipes or cotton balls and just water would be a better option.

6. Washing powder reaction - this will be easier to tell because it shouldn't be restricted to certain areas of the bottom, but would likely show up around the neck etc as well. But to be safe you can wash just using bicarb soda.