One concern parents have about diapers is diaper rash. The good news (if your cloth diapering) , is that cloth diaper babies are less likely to develop diaper rash.
DISPOSABLES: With disposable diapers rashes are often caused by baby sitting in a diaper way to long, perfummes in the diaper, that weird gel stuff inside the diaper (its a chemical compound designed to soak up liquid) or the stay dry layer. Different babies react differently to different brands although I hear the most complaints about Pampers. In fact when I gave birth in a Hospital (first two kids I didn't have a midwife), they used pampers and my baby had a rash in less then an hour. The nurse looked upset but told me some babies just react this way to that brand.
Lesson: disposable diapers have 3 major rash downfalls. 1. They are loaded with chemicals, 2. Stay dry layers, 3. They encourage parents to not change baby enough.
RASHES NOT RELATED TO DIAPERING:
Yeast: A rash caused by yeast looks like bad acne. It is usually caused by babies diet or (if breastfeeding) moms diet. Also if you and baby are nursing and there is a yeast infection you will both need to be treated. You should see your doctor / caregiver for dietary changes and treatment. Also check babies mouth for thrush. A nursing mom will pass a yeast infection to a babies mouth also. thursh is white and can be mistaken for milk in the mouth. During and after the yeast infection your cloth diapers need thorough cleaning (possibly stripping) and should be sun bleached so the UV rays can kill off any bacteria.
Food: sensitivity to foods can cause diaper rash. If your introducing foods to baby one at a time this will help lots. Often a sensitivity to a food will result in a diaper rash. The reason being is that food is touching babies skin via the poop. Eliminating the food should help. It is also important to let your child's caregiver know about the possible sensitivity so they can assist you in properly following up on this. For Native families like ours milk is the number one culprit for this. You can see if drinking just whole (homo) milk helps, but sometimes baby (and mom if nursing) need's to eliminate all milk and milk products.
Teething: sometimes teething causes a bit of rash, check to make sure there is no other reason. Treat with a rash care product. If it is teething you will likely notice a bit if rash on babies cheeks also.
OTHER DIAPER RASHES:
Several things about diapering can cause a rash. Lack or air (circulation, breathability) can cause a rash. diaper covers are the common culprit. If your cover or diaper has PUL or other non-breathable layers you may need to consider diapers and covers that are breathable. Many cloth moms who do use PUL covers use them only part time and avoid them in the summer. Clothing items such as baby leg warmers leave the diaper exposed but baby's legs covered. I have a post titled: SO EXCITED ABOUT BABY LEG WARMERS - clothes can be an issue when cloth diapering that covers Baby leg warmers and dressing a cloth diapred baby.
Number of diaper changes: sometimes the diaper needs to be changed more often. We have both disposable and cloth diapers now that can allow baby to pee for hours without being changed. Even if your diaper is dry, the urine is still there ands baby is still sitting in it. Please change frequently.
Ammonia: this can be built up in diapers as it is a by-product of urine. It can build up in Diapers that are not changed often (see above reason for a rash). Also if you wait to long to wash your diapers (longer then 3 days), dont use enough detergent, over or under fill your wash machine you may get ammonia build up. Also fleece and micro fiber are prone to this. Ammonia causes rashes.
Dried out or irritated skin: some materials do not belong next to babies skin. If it wicks away moisture (such as micro-fiber) it will wick moisture out of babies skin. This will leave baby with chapped bum just like a chapped hand in winter.
Also if you use to much detergent and it is being rinsed out it will build up in the diaper and may cause a rash. It also decreases diaper absorbency. Adding vinegar to your rinse can help prevent this problem.
If you have a rash on baby treat the rash with a rash care product. It is your choice what you use and maybe you want to experiment with various types and methods. When using a rash treatment use a disposable liner to protect the cloth diapers, liners etc. Some treatments such as coconut oil are safe for cloth and wont need a disposable liner.
Give the bum some air time! Taking off the diaper and exposing it to air is an old and proven way to help a diaper rash heal.
Consider diapering for circulation using wool covers or no covers over your diapers.
TREAT THE CULPRIT: Check all the above possibilities, when you know why there is a rash you can work to prevent it from re-occuring (except for teething). Check your diapers and liners! If they smell then ammonia is the problem. Treat all diaper products and develop a routine where this wont happen again. You might also need to choose more natural fibers.
*note: if you are frequently stripping diapers (as in you've done it more then once), you need help with your routine to prevent this. Also multiple strippings will wear out your diapers faster and lead to leaks.