Depends on both of them. If it is consensual, it is okay.

In the entirety, there can be two more issues people seem to have:

1. Moral:
   I would say, against all kind of activities that given a human being pleasure, the most prejudiced one by society and religion is s3x. Just because “it gives us pleasure, it must be a sin to do it more” mentality of all religions, therefore everything else related, such as masturbation, oral s3x, anal s3x etc automatically become bigger sin. So it depends how much both aduIts take this to their heart, because it cannot be changed by the opinion of an outsider and more likely to have a negative effect.
2. Hygienic:
   This becomes an issue for people who consider s3xual organs to be filthy, but it is just another part of the human body. As long as you wash it exactly same as your hands and legs, touching p3nis and v@gin@ is exactly same as holding hands. Now if one is using his mouth for oraI s3x this again is just another contact or exchange of body fluids and again same as exchanging body fluids while having s3x. So overall as long as both aduIts are clean and hygienic mostly every s3xual interaction is ok.