Well it's a very intimate question and like many human activities and behaviours is a little bit gross when written down and shared with others.
I'm sure it falls into the category of normal (as is; always cleaning up after sexual activity, choosing to masturbating in the shower and choosing not to masturbate and everything else that doesn't cause harm to yourself or others).
Is it hygienic? - no but standard sexual activity with a longterm partner can be even more unhygienic. Unhygienic sexual activity with a short-term or causal partner is unlikely to be safe - using a condom is essential.
Is it an imminent threat to your health? - no.
Is it a longterm threat to your wellbeing? - not unless you have underlying health conditions (a propensity for infection, weakened immune system, etc), it's part of a longterm behaviour (not changing sheets, cleaning clothes, bathing, washing hands after going to the toilet) or it's causing you worry or anxiety.
Is it more common practice when you are younger, on your own and if your threshold for hygiene is lower? - yes.
Is it worth worrying about? - no.