Is it ok to swallow a cum?

Hmmm....: When a woman swallows semen or sperm, her body just treats it as food (a small snack). It has no effect on her body, so if she shows some changes, it is merely by coincidence. However, life is never that simple. During the process of obtaining that semen, she might also obtain various viruses, bacteria, ureaplasma, etc..., from he who is the source of the semen. So, swallower beware.

Yes: If STDs have been ruled out then it is safe to consume as much as you want.