Rashes are tricky. That looks like it could be from heat, or if could be from a virus. My kids get a similar rash on their bellies and back when they get sick. Even regular colds can cause a viral rash. If it's not bothering him and he seems healthy, there's not much to do but keep an eye on it.
What is this? My son has little tiny bumps that were on his back, went away almost completely and now it's all over his chest and tummy - he spit up but no other symptoms (pic included)
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