I have never experienced this before as DD never had this problem. Both of my twin boys have a neck rash from milk. It is under their chin as well. We have tried diaper rash cream and vasoline. The doc gave us something to mitigate yeast infection but it doesn't stop the rash. Their necks are pink and the chubbier twins is much redder. We have bibs on them, prop them up at night and keep the bibs on. We tried using the receiving blankets but they always pull them and push them off. I am at wits end what to do. Baby A's neck is gonna start bleeding in a few days if I can't stop this.

. Everyone says they will grow out of it eventually but it is painful to watch this. It doesn't seem to be hurting them.
Re: Extreme milk rash around neck!! HELP!
this or Aquaphor ointment heals everything...they sell it at Target. I have used it on my DD neck when she gets red and it seems to heal within hours.
Just looked at the tube - it's called Baby Aquaphor healing ointment advanced therapy. Sold in the baby aisle at Target. White and navy tube. I also use this when DD scratches her face and it heals very quickly.
We are dealing with the same thing. We struggle to get the area clean. We have found that tummy time up on the kitchen table with me or my husband kneeling on the floor looking up helps us get a really good view and ability to clean better.
Our pediatrician suggested hydrocortisone ointment.
Aquaphor is great - just be sure the neck area is DRY when you apply it - as it will seal moisture IN & make it worse. Hydrocortisone works, too.
My kiddo has extra sensitive skin & even lotions seem to irritate her. (DD1 did not, so this has been such a pain to figure out what works on her skin) But aquaphor is fantastic for her sensitive skin.