Anorexia is an eating disorder characterised by voluntary starvation and exercise stress. Anorexia is a complex disease, involving psychological, sociological and physiological components. A person who is suffering from anorexia is known as an 'anorexic,' 'anorectic,' or the less common 'anoretic.' Anorexia simply refers to the medical symptom of lost appetite. Anorectic and anoretic also refer to appetite-suppressing drugs.

The causes of anorexia are a matter of debate in medical circles and society in general. General perspectives fit between the poles of it being physiological or psychological (with the potential for sociological and cultural influences being a cause to various degrees) in origin. Many now take the opinion that it is a mix of both, in that it is a psychological condition which is often (though not inherently) borne of certain conducive neurophysiologic conditions.

Anorectic people may display the following signs and symptoms:

• be too thin and/or appear to have lost weight;
• be secretive about their eating and try to not eat whilst being around others;
• eat in a ritualistic nature (This can encompass taking abnormally small bites, cutting food up into abnormally small pieces, being sullen during mealtimes, staring at their food whilst eating, holding cutlery in odd ways or at strange angles at times, or eating slowly, especially when putting food into the mouth.);
• look longingly at or pay abnormal attention towards food but not eat it;
• cook wonderful meals for others but avoid eating the food they've made themselves;
• say they're too fat when they are not;
• have dry skin and thinning hair;
• suffer from poor health and sunken eyes;
• have grown lanugo, a thin hair that grows all over their body as a natural physiological reaction to severe starvation that serves to keep the body warm in the absence of fat;
• possess an extensive knowledge about the food energy contents of the different types of food, and the energy-burning effects of each form of exercise;
• faint or otherwise pass out (an effect of starvation);
• have amenorrhea, the absence of menstruation.

A person can be anorectic without displaying all of the above signs.

Generally:

• Voluntary starvation
• Exercise stress
• Obsessive-compulsive behavior

• Negative impact on the immune system
• Negative impact on the Central Nervous System
• Serotonin deficiency

The following is considered the "textbook" definition of anorexia to assist doctors in making a clinical diagnosis. It is in no way representative of what a sufferer feels or experiences in living with the illness. It is important to note that an individual can still suffer from anorexia even if one of the below signs is not present. In other words, it is dangerous to read the diagnostic criteria and think either oneself or others must not be anorectic because one or more of the symptoms listed are not present.

• Refusal to maintain body weight at or above a minimally normal weight for age and height (e.g., weight loss leading to maintenance of body weight less than 85% of that expected; or failure to make expected weight gain during period of growth, leading to body weight less than 85% of that expected).
• Maintaining excessive physical activity.
• Intense fear of gaining weight or becoming fat, even though underweight.
• Disturbance in the way in which one's body weight or shape is experienced, undue influence of body weight or shape on self-evaluation, or denial of the seriousness of the current low body weight.
• In postmenarcheal females (women who have not yet gone through menopause), amenorrhea (the absence of at least three consecutive menstrual cycles).

Restricting Type: during the current episode of anorexia nervosa, the person has not regularly engaged in binge-eating or purging behavior (i.e., self-induced vomiting or the misuse of laxatives, diuretics, or enemas).

Binge-Eating Type or Purging Type: during the current episode of anorexia nervosa, the person has regularly engaged in binge-eating OR purging behavior (i.e., self-induced vomiting or the misuse of laxatives, diuretics, or enemas).