It could be eczema/heat rash. My daughter had the same issue and I brought her to a derma. Was told that she has baby eczema and need to constantly apply moisturiser and wipe down areas that could get irritated by sweat on hotter and humid days more often throughout the day
maybe it's eczema? when my girl had rashes and see paediatrician,she recommend to change cetaphil gentle cleanser and her rashes slowly reduced.
Rashes doesn't bother your baby, but please apply moisturizer on his body, suspect might be heat rashes due to sg humid weather
Change to BB detergent, find those with fragrance and chemical free. You can try alobaby milky lotion, it works even for face
My girl encounter this too. Pediatrician recommend QV baby wash. it worked for her.
Try to change detergent
Haslieya