Chocolate: It's a smooth, creamy, melt-in-your-mouth confection.

It's the ultimate indulgence that also can be your worst addiction.

For some, the chocolate craving is simply a result of its being a tasty treat associated with pleasure, even romance. It is used often to reward good behavior or win another's favor.

But for others, overindulgence can exacerbate health conditions such as high cholesterol, diabetes and obesity, or be a sign, as eating disorders can be, of a psychological problems like depression, stress or anxiety. Scientists are still studying whether there is a physiological reason humans crave chocolate.

"Sometimes it can affect someone's life to the point it becomes a real problem," says Thomas Deahl of the University of Texas Health Science Center in San Antonio.

Studies show that twice as many women as men crave chocolate and sweets. Men are more likely to crave salty, high-fat food, Deahl says. The reasons are unclear, although some studies point to women's hormonal changes, which may trigger some cravings.

Each year a typical American eats nearly 12 pounds of chocolate.

The comfort quality of chocolate is enhanced by the fact that cocoa butter, the key fat in chocolate, melts at body temperature, giving it that "melt-in-the-mouth" quality, Deahl says. The creamy texture and taste add to the pleasurable sensation of eating chocolate.

"If I have one piece, I'm going to have more. It tastes so good you just have to have another piece," says Sue Conn of Colorado Springs, Colo., a weight control consultant who has seen people struggle with food cravings, particularly for chocolate.

"Sugar makes you want more sugar. For some people it's terrible and I'm one of them," she says. "We usually want it when we are having a feeling we don't want to have." Eating chocolate makes you feel like you are pampering yourself, she says.

Some researchers theorize there is something in chocolate the body needs or wants. Roasted cocoa contains 50 compounds that can stimulate changes in body chemistry--but most are found in higher amounts in other foods.

For instance, N-acylethanol-amine produces a relaxing narcotic effect. "But you would need to eat a lot of chocolate--about 27 pounds--at once to have a pharmacological effect," Deahl says. "There is more of it in soybeans and hazelnuts, but people don't crave those like they do chocolate."

Another chemical, phenylethylamine, works like an amphetamine and can improve mood in some depressed patients. "But the amount in chocolate is much lower than in cheese and salami," Deahl says. "Why don't they crave cheese and salami sandwiches instead?"

According to Deahl, low levels of chemicals such as serotonin, dopamine and norepinephrine in the brain can cause depression, insomnia and food cravings. Scientists, he says, are still trying to pinpoint the possible relation to eating chocolate and changes in brain chemistry that raise or lower those chemical levels.