Bad Breath, is an unpleasant-smelling breath. It is also called halitosis. It can occur occasionally, or it can be a chronic condition.

Food: It is the primary source of bad odors that come from the mouth. Foods like garlic, onion, exotic spices (such as curry), and few types of cheese, fish, acidic beverages such as coffee can leave a lingering smell.
Tobacco products: Smoking and chewing tobacco can leave chemicals that remain in the mouth.
Poor dental hygiene: Not brushing or flossing regularly leave the food particles in the mouth, which further rot and cause bad odors. Poor dental care can lead to a buildup of plaque in the mouth, which causes an odor of its own. This could further lead to various gum diseases as well.
Health problems: Any problem associated with respiratory tract or digestive tract, like sinus infections, pneumonia, sore throat, tonsil stones, bronchitis, diabetes, acid reflux, lactose intolerance, other stomach problems, and some liver diseases or kidney diseases may be associated with bad breath.
Dry mouth: Saliva helps moisten and cleanse the mouth, and when the body does not produce enough saliva, bad breath may result. This could be caused due to some medications as well.
Mouth infections: Cavities, gum disease, or impacted teeth may cause bad breath.
Dentures or braces: Food particles not properly cleaned from appliances such as braces can rot or cause bacteria and odor. Loose-fitting dentures may cause sores or infections in the mouth, which can cause bad breath.
Morning breath: Bad breath in the morning is very common. Saliva production nearly stops during sleep, allowing bacteria to grow, causing bad breath.
Pregnancy: Nausea and morning sickness during pregnancy can cause bad breath. Dehydration during pregnancy can be another reason.
Home Remedies
Fennel seeds

- Chew fennel seeds every time you have meals. This not only avoids bad breath but also helps in digestion.
- Having a clove and few pods of cardamom along with fennel seeds has a lasting impact and keeps the mouth fresh for a long time
- You can also make a tea by adding 2 tsp of crushed fennel seeds to 1 cup of boiling water. Let it steep, strain and drink it
Baking soda

- Take 2 tbsp of baking soda and dip your toothbrush in it
- Brush your teeth after normal brushing cycle, to having prolonged fresh breath
Cinnamon

- Add 1 tsp of cinnamon powder in 1 glass of water
- Boil this for 10 minutes and add 2 bay leaves and 1 cardamom
- Strain this water and use it to wash your mouth twice a day
Apple Cider Vinegar

- Mix 1 tsp of Apple Cider Vinegar in 1 glass of warm water
- Use this to gargle twice a day