Probably you don't drink enough water or live in a relatively dry area. Other major reasons include:
- Dehydration. Any condition that causes dehydration, such as excessive sweating, fever, diarrhea, vomiting, and burns will often lead to cases of dry mouth.
- Lifestyle. Chewing or smoking tobacco can reduce the amount of saliva your mouth produces and make cases of dry mouth worse. If you are always breathing with an open mouth, it can aggravate cases of dry mouth.
- Aging. Naturally, aging does not lead to dry mouth. However, as people get older, they tend to take more medications that may leave them with dry mouth, and they are more prone to diseases that result in dry mouth.
- Side effects of some medications. A common side effect of most prescription and nonprescription drugs is dry mouth. Drugs used for treating medical conditions like anxiety, depression, allergies, pain, obesity, colds, hypertension, epilepsy, diarrhea, psychotic disorders, nausea, asthma, urinary incontinence, and Parkinson disease may result in mouth dryness. Muscle relaxants and sedatives can also have dry mouth as one of its side effects.
- Side effects of certain infections and diseases. Certain medical issues like HIV/AIDS, diabetes, cystic fibrosis, Alzheimer's disease, mumps, anemia and Parkinson disease all have dry mouth as a common symptom.
- Side effects of some medical treatments. Damaging the gland responsible for making saliva, can affect the quantity of saliva your mouth produces. For instance, such damages could be as a result of certain radiations that affect the head or neck such as chemotherapy for treating cancers.
- Damage to the Nerves. Dry mouth can also be as a result of damage to the nerves in your head or neck area as a result of surgery or injury.
(The last two situations are quite rare, and I don't think they are your situation. Just put it here as reference.)
Here are some tips that can help you get relief from symptoms of dry mouth:
- Drink water and drinks free from sugar or suck chips of ice all through the day to keep your mouth moistened, and take lots of water when eating your meals to make chewing and swallowing easier.
- Don't breathe through your mouth, make use of your nose while breathing. If you snore in your sleep, seek treatment to help you stop breathing through with your mouth open.
- Use a room humidifier and add some moisture to the atmosphere.
- Avoid taking tobacco, alcohol and caffeine. All these can lead to irritation and dryness in the mouth. If you make use of a mouthwash that has alcohol, look for an alternative.