(B) Ageusia # Ageusia is the loss of taste functions of the tongue, particularly the inability to detect sweetness, sourness, bitterness, saltiness, and umami (the taste of monosodium glutamate). It is sometimes confused for anosmia--a loss of the sense of smell. Because the tongue can only indicate texture and differentiate between sweet, sour, bitter, salty, and umami most of what is perceived as the sense of taste is actually derived from smell. True aguesia is relatively rare compared to hypogeusia--a partial loss of taste--and dysgeusia--a distortion or alteration of taste.> Causes of Ageusia:> Neurological damage: Tissue damage to the nerves that support the tongue can cause ageusia, especially damage to the lingual nerve and the glossopharyngeal nerve.> Neurological disorders such as Bell's palsy, Familial dysautonomia, and Multiple sclerosis cause similar problems to nerve dam- age, as do certain infectious conditions like primary amoeboid meningoencephalopathy. The lingual nerve (which is a branch of the trigeminal V3 nerve, but carries taste sensation back to the chorda tympani nerve to the geniculate ganglion of the facial nerve) can also be damaged during otologic surgery, causing a feeling of metal taste.> Problems with the endocrine system:> Deficiency of vitamin B3 (Niacin) and zinc can cause problems with the endocrine system, which may cause taste loss or alteration. Disorders of the endocrine system, such as Cushing's syndrome, hypothyroidism and diabetes mellitus, can cause similar problems.> Ageusia can also be caused by medicinal side-effects from antirheumatic drugs such as penicillamine, antiproliferative drugs such as cisplatin, ACE inhibitors, and other drugs including azelastine, clarithromycin and zopiclone.> Other causes:> Local damage and inflammation that interferes with the taste buds or local nervous system such as that stemming from radiation therapy, glossitis, tobacco abuse, and denture use also cause ageusia. Other known causes include loss of taste sensitivity from aging (causing a difficulty detecting salty or bitter taste), anxiety disorder, cancer, renal failure and liver failure.