Cream/lotion For Dark Neck

It could just be due to friction between skin folds in which case retinoid-based ointments should help a little bit. But it's possible that the dark skin around your neck is a condition called Acanthosis Nigricans. It is usually the result of insulin resistance or diabetes. It can range from really mild to extremely severe cases depending on the severity of the diabetes. I think you mentioned you had gestational diabetes and this developed after your pregnancy. Do you also have darker underarms and ankles? If so, then this definitely due to blood sugar fluctuations. There isn't a specific treatment for it but you should still see your doctor about it. It can be reversed to a large extent by improving insulin sensitivity. If you eat low-carb and maintain an even blood sugar level for a few months the skin should slowly start lightening up.