What Cause Bumps On The Head Of The Penis?

Last night, I masterbated and after I've finished. There are little red bumps on the head of penis. It looked like herpes. But there wasn't any of herpes' symptoms. It doesn't itch, burn, or hurt. Today, it looks like it's clearing up! And it is painless. I was just freaked out, because when I first saw it. It looked like little red pimples on my penis head. Just only a few small ones, nothing big. So my question is? Is it because of irritation, and I am not circumcised.