When I was but a silly teenager, with any notions of becoming an acupuncturist far in my future, I had a Yin-Yang symbol tattooed on my ankle. At that time, I thought I was displaying my inner wisdom and worldliness by having a symbol of balance permanently engraved on my foot (and at least it was preferable to option number two: a mooning leprechaun raising a beer glass over his shoulder). I had no idea of the real significance that lies behind the Yin-Yang symbol, or of all the years and money I would spend becoming educated on the topic. Life is ironic, isn't it? Yin and Yang are the cornerstones of all the theories that lie behind Traditional Chinese Medicine (TCM), and the concept is both completely simple and utterly complicated. It is simple, because it is quite easy to see the distinction between the categories. Its complexities are due to its all-encompassing nature. Every single thing in existence can be broken down into groups of Yin and Yang, and into varying degrees of such. In fact, there is no pure Yin and Yang-it's like trying to figure out what the smallest item in existence is.
In TCM theory, the characteristics of Yin are soft, cold, quiet. A person with a Yin constitution might be introverted and soft-spoken, larger-framed, and pale. This is a person with little "fire" in their system (fire and heat are Yang characteristics). So, they might add "Yang" to their system by covering up with blankets, overdressing, and craving warm food and drinks. They would tend to think before speaking, move and talk more slowly, and be more relaxed in general.
A Yang person, on the other hand, might have a more wiry frame, speak loudly and quickly, and jump into action without thinking first. They are usually hot, sweating more and tending to wear less clothes. You know those people who can't sit still for more than a minute, who feel the need to pace around the room as they talk? These are Yang constitution types. Hyper, energetic, and fiery-natured, the Yang types tend to get more done than Yins, but can burn out easily.
Now, as I've said, there is no perfect Yin or Yang-we all have both qualities in us to a certain degree. Our constitution depends on which of the two we possess more of in our nature. And we need both, because one cannot exist without the other. If there is no up, there can be no down, and so it also is with Yin and Yang. .
When it comes to health, Yin and Yang need to be in relative balance, or dysfunction will occur. Let's look at the example of sleep. Sleep in general is a very Yin function (remember, think of Yang as "action", and Yin as "rest". They counterbalance each other.) If there is too much Yin in the system, the person will sleep too much, fall asleep during the day, or be unable to fully wake up when morning comes. If there is too much Yang, the person's mind and body will be too active to fall or stay asleep. As acupuncturists, we have the tools to build and disperse Yin and Yang, bringing them closer to a state of absolute balance.
Or, as another example, let's look at menopause. The symptoms of menopause derive from the natural depletion of Yin. As the Yin is slowly worn away,the Yang becomes more prevalent. The result? The patient experiences symptoms of heat (night sweats, hot flashes), and reduction of fluids such as menstrual blood and vaginal lubrication (the distribution of the fluids of the body is a Yin property). Irritability, agitation, and anxiety are also all symptoms of heat manifesting in the personality.