Taste - impaired or Bad Mouth Taste.

From: http://www.nlm.nih.gov/medlineplus/ency/article/003050.htm

Taste impairment means there is a problem with your sense of taste. Problems range from distorted taste to a complete loss of the sense of taste. However, a complete inability to taste is rare.
Considerations
The tongue can detect only sweet, salty, sour, and bitter tastes. Much of what is perceived as "taste" is actually smell. People who have taste problems often have a smell disorder that can make it hard to identify a food's flavor. (Flavor is a combination of taste and smell.)
Taste problems can be caused by anything that interrupts the transfer of taste sensations to the brain, or by conditions that affect the way the brain interprets these sensations.
Causes
Aging (the number of taste buds decrease with age)
Bell's palsy
Common cold
Flu
Gingivitis
Heavy smoking (especially pipe smoking)
Injury to the mouth, nose, or head
Mouth dryness
Nasal infection, nasal polyps, sinusitis
Pharyngitis
Salivary gland infections
Side effects of medicines, including antithyroid drugs, captopril, griseofulvin, lithium, penicillamine, procarbazine, rifampin, vinblastine, and vincristine
Sjogren syndrome
Strep throat
Vitamin B-12 or zinc deficiency

Home Care
Follow prescribed therapy, which may include a change or changes to the diet. For taste problems due to the common cold or flu, normal taste should return when the illness passes. For smokers, stop smoking.
When to Contact a Medical Professional
Make an appointment with your doctor if your taste problems do not go away, or if abnormal tastes occur with other symptoms.
What to Expect at Your Office Visit
The doctor will perform a physical examination and ask questions, including:
Do all foods and drinks taste the same?
Do you smoke?
Does this change in taste affect the ability to eat normally?
Have you noticed any problems with your sense of smell?
Have you recently changed toothpaste or mouthwash?
How long has the taste problem lasted?
Have you been sick or injured recently?
What medicines do you take?
What other symptoms do you have? (For example, appetite loss or breathing problems?)
When is the last time you went to the dentist?
If the taste problem is due to allergies or sinusitis, the doctor may give you medicine to relieve the stuffy nose. If a medicine you are taking is to blame, your doctor may recommend that you change your dose or switch to a different drug.
A CT scan may be done to look at the sinuses or the part of the brain that controls the sense of smell.
Alternative Names
Loss of taste; Metallic taste; Dysgeusia
References
Wrobel BB. Clinical assessment of patients with smell and taste disorders. Otolaryngol Clin North Am. Dec 2004; 37(6):1127-42.
Doty RL. Effects of drugs on olfaction and taste. Otolaryngol Clin North Am. Dec 2004; 37(6):1229-54.
Update Date: 3/3/2009
Updated by: James L. Demetroulakos, MD, FACS, Department of Otolaryngology, North Shore Medical Center, Salem, MA. Clinical Instructor in Otology and Laryngology, Harvard Medical School. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.

Blogger Comment:
When there is change in taste look for nasal causes since impaired smelling cause impaired taste. Then look for mouth causes look for gingivitis, dry mouth, pharyngitis, thrush.. Most of mouth causes can be seen in the mouth. If no nose or mouth causes in clear in history and examination inquire about new medication that can cause the problem as above, acid reflux which classically cause bitter sensation in the mouth and check vitamin B12 and blood zinc levels for deficiencies.