More often than not, it will be something that is far less serious but a condition you will want to get checked out nevertheless. Here are just some of the non-infectious and infectious causes your doctor may investigate. A non-infectious penile skin condition is one that you cannot get it from or pass it to another person. While this shouldn't suggest that you can ignore it, a non-infectious skin condition tends to be less serious than an infectious one. While more irritating than problematic, the condition may be caused by harsh chemicals, abrasion, or an allergen your doctor can help identify.
If what you're seeing looks like a symmetrical swelling near the base of his penis in front of the scrotum, what you see is likely the bulbus glandis. This structure is a normal part of the male dog's anatomy. The bulbus glandis swells during mating which causes the dogs to tie or 'lock' together during the act. It may swell when the dog is excited, even in a neutered dog.