Traditional Culture Encyclopedia - Photography major - Is it harmful for friends to suck nipples?

Is it harmful for friends to suck nipples?

Sucking nipples is part of foreplay. Can let women enjoy wonderful sex life. But sucking nipples for a long time will make them black. If this is harmful, then this is unique.

If you are satisfied with it, please give it to us. Oh, O(∩_∩)O Thank you.