Ay, mama, mahirap sabihin talaga just by description kasi maraming possible causes ng skin changes sa babies, puwedeng prickly heat, allergy, eczema, or just normal baby skin stuff talaga! A few of us mums noticed na ang init at sweat ay nag-trigger ng rashes sa arms ng babies natin, pero hindi lahat ganyan. Better to check with your pediatrician para ma-diagnose properly at ma-ease ang mind mo, lalo na kung may itch or discomfort ang baby mo, they can give you the right treatment agad! In the meantime, make sure the area stays clean and dry, and avoid tight long sleeves kung mainit. Sending you a hug, mama, I know ang worry pag makita ng something unfamiliar sa skin ng baby!