I have a rash on my arms what should i do?

i need some advice i have a rash on my arms there little speckled dotes that reappear every once in a while i think it may me a food rash of some sort they don't itch i really can't feel them at all and I'm only 11 should i tell my dad or mom? my brother knows though that's what he thinks it is to because he has the same thing it's just on his legs