If he hasn't taken a shower right before we make love, his penis smells. I assume it is the secretions getting stuck under the foreskin. I'm really very curious to know if this is a problem.
Circumcision removes the foreskin from the penis.
Men with uncircumcised penises need to pull back their foreskin and wash the area underneath at least once a day. This is probably what you are noticing on your boyfriend's penis. The area under the foreskin is also ripe for bacterial growth. Infections can easily develop under the foreskin if it isn't pulled back and washed. A yeast infection, which has symptoms that include redness, swelling, and a pasty discharge, is also a possible occurrence when the uncircumcised penis is not cleaned properly.