soo I dont know what to think I dont even know is this is a rash but my kid has a line of red bumps like where you began to tighten the diaper... but it's literally in a line... i check every where else and I am a user of aquaphor, and I use it on his parts, I just never thought to put it on his back... Its a part that I'm sure can easily be missed because it's like near mid like I said were you tighten the diaper... the only changes I made is I took him to the pool for the first time, upped his diaper size from size 2 to 3, and I Kirkland to Pampers... I know it's not a brand rash because I was changing diapers since he came out of the hospital to get a feel of which diapers worked for us.. lol.. but please help