Our 3-month old son has bad diaper rash. We're putting a lot of the cream on each time we change his diaper. How long will it take before this goes away?
If it doesn't look to be getting better after 3 days, you should contact your pediatrician. Also contact your pediatrician if there are pus-filled blisters, if the rash is in the folds of skin around the legs, or if the rash is bleeding.
Diaper rash is typically caused by irritation from the moisture from the baby's waste, but it can also be caused by allergic reactions to perfumes or other chemicals in the diapers, wipes, or lotions you use. A yeast infection of the skin can also result in diaper rash, in which case the pediatrician will need to prescribe a remedy.
For regular diaper rash, treatment with a moisture blocking cream will usually clear up the rash within a day or two. In severe cases, you might want to consider letting the diaper area air dry for about 15 minutes before putting a fresh diaper on (put the baby on a mat or towel you don't mind getting soiled!).
In my experience, there's diaper rash, and then there's allergic rash. My baby's diaper rash (even when it's caused by teething) goes away in 1-2 changes as long as we put cream on it, like Desitin, which you can get from drugstore.com. The severity you describe makes me concerned that the diaper rash you're describing is not actual diaper rash, but is allergic rash.
Allergic rash seemed very different from regular diaper rash, but all we realized at the time was that it was a weird-looking rash. A typical diaper rash for my baby is all over her bottom. The allergic rash was a very tightly-concentrated rash close to the anus. It did not go away easily or quickly, and before we realized it was due to an allergic reaction to dairy, it got to the point where the skin was raw and would bleed a bit when we cleaned her bottom. The rash did not clear up until after we wised up after a few days and eliminated all dairy from her diet.
One note is that many creams and ointments contain lanolin. This is basically derived from sheep. Plenty of people are allergic to wool and may react to lanolin. (I'm allergic to wool and finding a cream for breastfeeding that had no lanolin yet was safe for the baby was a job and a half; I used Nuk.) Aquaphor is commonly recommended for many baby rashes--including severe diaper rash--but contains lanolin. So if you are using a lanolin-based cream you may want to switch to something else to eliminate the possibility of the cream causing a reaction.
If your baby is breastfed and the rash is persisting, you may want to first eliminate lanolin, and then after that try an elimination diet for his mom. I'd recommend allergy testing but unfortunately, I know from personal experience that it is faulty. I'm allergic to peanuts and have gone into anaphylactic shock upon eating one, yet my skin and blood tests come back negative. Allergy tests often generate false negative results. The link above about elimination diets can be very helpful. If the baby is formula-fed, you may want to talk to the pediatrician about switching formula brands or even a hypo-allergenic formula if the rash continues and you and the doctors feel allergies are to blame.
Typically, babies at 3 months aren't given solids but if you are giving solids, you'll want to talk to your doctor about allergy concerns there, as well.
Good luck and I hope it is regular diaper rash, not the allergic rash kind my daughter had!