The coating on the tongue indicates the level of hydration.
When the body isn't hydrated, the tongue immediately looks and feels dry. You may have some of the following symptoms: insomnia, vivid dreams, hot flashes, constipation, dry skin, thirst, heartburn, or hunger. It's common that dehydrated tongues to also struggle with hyperactive thyroid, menopause, high blood pressure, depression, anxiety, or gastric ulcers.
If you have a thick, greasy coating, it is an indicator that your body has lots of dampness and fluid. This is an expression of polarities. Either you are consuming too many greasy, cloying foods that aren't right for your body and your body can't get rid of the grease or because you are already dehydrated and the water capacity is now turbid and thick, causing a different level of dehydration. With this tongue coating, you may suffer from symptoms such as heavy arms and legs, bloating, lack of energy, stiff joints, weight gain, sluggish bowel movement. These people usually have high cholesterol or fatty liver.
A thick yellow coating, right in the center of the tongue, means your body is dehydrated and can't digest your food. You may have some of the following symptoms: body heat, sweating, body odor, and bad breath, yellow urine, constipation, pungent or dark stool, pass lots of gas, bloating, red face, vivid dreams or nightmares, or insomnia. These people may also suffer from high blood pressure, high cholesterol, diabetes, liver or gallbladder disease.
An uneven coating indicates an issue with hydration in your stomach and liver. You may suffer from symptoms such as heartburn, stomach pain, interrupted sleep, vivid dreams, dry skin, and discomfort of the side of the body. Health problems that can accompany this include liver and stomach disorders or gastric ulcers.