Sounds like heat rash or any other common pore ailment (theres a list of them).
They only appear on pores where you have hair folicles right? Climate change would probably be the only permanent solution. Otherwise, anti-bacterial soap, rinsing, some lotions, etc... they come and go on my legs. Tiny (barely visible) and sporadic.
See a dermatoligist if they really annoy you or you have a lot of them. Its genetics, but heat/sweat tends to create more of them since your pores are getting clogged and irritated.