Hi there, Thank you for choosing HCM for your query. As you said your infant has had a red rash on her neck for about 3 months and her skin under her chin is brown patchy looking. There could be a few reasons for the same. If your infant has had lot of drooling especially since this is the age group for teething, then there is a likelihood that the saliva may go and sit in the neck fold and under the chin causing constant wetness in that area, which predisposes to a fungal infection and will need to be treated for the same. Also, some children are more predisposed to getting eczema especially if one of the parents has eczema or had asthma in their childhood. This can cause red rash in the skin folds which may worsen with weather change or with excessive sweating and over time the skin looks thickened and hyperpigmented if not treated. Eczema treatment requires good hydration of the skin with lotions/vaseline and also if the skin is very raw at times will need steroid ointments with a prescription from a doctor and under their expert advise. I would recommend that since your child s rash is not getting better over time and has spread, you should see her pediatrician again or a dermatologist for an expert opinion to have her examined and advised treatment accordingly. Hope this helps. Regards, Dr. Sumeet.