Very few people appreciate tongues-or at least, they lack appreciation for their own. I know that it's wet, and slimy, and sometimes covered in remnants of your last meal...but it's a great diagnostic tool to determine what has been going on with your health.
I found this chart online to give you an idea of some of the things we acupuncturists look for when we have you stick out your tongue. Notice how red some of the tongues are? That means that there is excess heat in the body. Depending on where the redness is located, we can also determine what organ system the heat is affecting. A red tongue tip could mean heat in the Heart or Lungs. If the center of the tongue is red, there is heat in the center of the body-namely, the digestive organs. The sides of the tongue can be red if there is heat in the Liver or Gallbladder. And if the back of the tongue is red, there can be heat in the Kidneys, Bladder, or Intestines.
A "normal" tongue has a thin white coat. If the coat is yellow, again, it signifies heat (particularly damp heat). A thick coating means that the food or fluids of the body aren't being processed efficiently. It can also mean that there is an external pathogen affecting the body. The thicker the tongue coat, the more serious the condition.
A purple tongue body is stagnation, and it is probably the color that I see the most frequently in patients. Everyone seems to have some sort of stagnation going on.
A pale tongue can be qi or blood deficiency (usually this type of tongue seems rather thin, as well. A brown coating means that there is severe heat in the system; if the coat is gray or black, the condition is usually serious. And a geographic coating means that there has been damage to the Stomach-either to the Stomach qi (which is the main source of the body's qi), or to the Stomach Yin.
If you're bored at work and sick of killing time on Facebook, here's a fun quiz to give you a very basic idea of your own tongue diagnosis: http://beyondwellbeing.com/herbs/tongue-diagnosis.shtml.Please note that this is just for entertainment purposes and may not be an accurate indicator of your own health issues. It's simply a guide to what we acupuncturists look for, and shouldn't be taken seriously as a diagnostic tool. Also note that you probably shouldn't take the quiz while eating...or if you're squeamish.