Is he under any type of long term medication and what's his age. Any significant medical history? Any bad breath/bleeding gum? There may be presence of food deposition caUsing calculus formation lead to gum irritation and inflammation. Betadine mouthwash once a day after meal for 2 weeks. Followed by that  once in every two days.after using mouthwash don't rinse, eat or drink anything for 15 mins. And followed by that brush teeth thoroughly. If no history if medication. Pls consume these medicines and visit dentist. After food, Doxycycline 100, once a day for 10 days. Metrogyl 400, thrice a day for 3 days. Roles D, once a day,for 10 days, before food/empty stomach.

It may be due to long term medication side effect or having food loadgement under the gum,

This is gingival hyperplasia (overgrowth of gum tissue around the teeth) it is often a symptom of poor oral hygiene. Or a side effect of using certain medications. If left untreated can cause gum disease.