I think its best that the person does know ( once out of love ) I think a lot of people are looking for bleeding gums as a sign and bad hygiene as the result, when there could be other factors.
Recently I realize a bad taste in my month, I was really surprise and had it check. Because of that detection, I discovered a tiny tonsil stone ( can be multiply, and vary in size ). One of the ways it is form is breathing through the mouth, allowing bacteria to stick to the tonsils.
Last month my family started asking me why was I breathing heavy, and the topic of asthma came up, so I started breathing through my mouth to make my breathing less noticeable. The last week at work I was organizing the stock room, breathing in all that dust and bacteria, and not realizing the effect it was having.
With the stone gone I had to Admit the problem with my breathing, I found out my inferior turbinates are swollen (result of allergies), which is blocking my nasal passage.
Sometimes when we ignore things, we actually affect other areas of the body. hopefully the swelling of my Nasal conchae go down, I dont want to go under the knife..
Its best that the person knows, because the body could be saying “Quit ignoring me, something is wrong “
There is more to it than gingivitis, like a person who constantly has a cold will have bad breath because of the nasal drip, which is mucus settling behind the mouth. And the products selling on the shelve, actually assist because they contain alcohol which dries the mouth.
Also diet, undigestible protein could be the cause. Snoring also causes bad breathe it forces air over oral and throat tissues.
If the person is a friend, they would take it in love.