The active ingredients are simple: just salt and water. You can purchase it over the counter without a prescription. Then, if your nose feels dry, give it a quick spray. Put 1–2 drops of spray into each nostril every 2–4 hours so you don’t lose any moisture.  If it is just salt and water, it is safe, won't irritate your mucous membranes, and shouldn't cause side effects. This is excellent in winter during flu season. You can bring a small bottle of saline spray with you to use at work and in the car. You can use it three times a day if you need to.  Some commercial saline sprays have preservatives in them which may irritate your membranes; however, the preservatives also prevent the growth of bacteria and other contaminants. Check the ingredients on the packaging. If it contains preservatives or ingredients other than salt and water, then be very careful not to use it more often than recommended by your doctor or the manufacturer's instructions. If you want to use preservative-free saline, find one that uses a no backflow method or has a more acid pH to decrease bacteria. You can make a homemade saline solution, but it can be difficult to get the proper balance of salt to water, which can lead to dry sinuses. But, if you have no other choice, you can try making your own saline. Add a teaspoon of salt to a quart of water. Then boil it for 20 minutes to sterilize it. While it may be tempting to use an antibiotic ointment like Neosporin, you should avoid overuse of antibiotics. Most colds and flu are caused by viruses, not bacteria, so the antibiotics will have no effect. Instead, spread a thin layer of a saline-based gel to the inside of your nose to keep it moist. Use a clean cotton swab to apply the ointment. Lightly coat the Q-tip with ointment and then apply it to the inside of your nostrils. Do not use so much that it gives you the sensation of a stuffy nose. Nasya oil is a type of moisturizer used to keep nasal passages moist and clean. Tilt your head back or lie down so you’re looking at the ceiling....

TL;DR in Vietnamese:
Giữ ẩm cho màng nhầy bằng nước muối sinh lý xịt mũi. Bôi nước muối sinh lý dạng gel. Làm dịu màng nhầy bị kích ứng bằng gel lô hội. Đừng bôi Vaseline, dầu khoáng hoặc sản phẩm dạng dầu khác (như dầu dừa) vào bên trong mũi.