Is there a different type of primer i have to use when running PCR with genomic DNA compared to cDNA?

Im still in school but when i run a PCR, I normally isolate RNA first then RT to cDNA and run PCR with that. This time i isolated the genomic DNA from the sample and ran PCR using the beta-actin primer i always used. Dimers were faintly visible on my gel but nothing really came up like it normally would have or should have. I was told that when running PCR with genomic DNA, a different kind of primer had to be used; one that is specific to genomic DNA. Im confused as to why it would matter or if it matters at all.