Tanning addiction
Tanning addiction is a rare syndrome where an individual appears to have a physical and/or psychological addiction to sunbathing or the use of tanning beds.  The mechanism of the addiction is unknown at this time.

# Medical evidence
In 2005, a group of dermatologists published a study showing that frequent tanners experience a loss of control over their tanning schedule, displaying a pattern of addiction similar to smokers and alcoholics. 
Biochemical evidence indicates that tanning addicts are addicted to an opioid release experienced during tanning. When frequent tanners took an endorphin blocker in a 2006 study, they experienced severe withdrawal symptoms, while infrequent tanners experienced no withdrawal symptoms under the same conditions. 

# Tanorexia
Tanorexia is the term often used to describe a condition in which a person participates in excessive outdoor sun tanning or excessive use of other skin tanning methods (such as tanning beds) to achieve a darker skin complexion because they perceive themselves as unacceptably pale.  The syndrome is different than tanning addiction, although both may fit into the same syndrome and can be considered a subset of tanning addiction.
Although the term "tanorexia" has been commonly used by the media and several doctors to describe the syndrome, both the word and syndrome have not been widely accepted by the medical community, and is considered a slang by many.  The term was coined after the medical condition anorexia nervosa, a disorder characterized by low body weight and body image distortion with an obsessive fear of gaining weight. It can be likened to the common practice of adding the suffix "-oholic" (from the term alcoholic) to the end of any action or food someone enjoys extensively and often (e.g. "choco-holic," "golf-oholic," "shop-oholic," etc.).
Serious cases of tanorexia can be considered dangerous because many of the more popular methods of tanning (such as those mentioned above) require prolonged exposure to UV radiation, which is known to be a cause of many negative side effects, including skin cancer.
Extreme instances may be an indication of Body dysmorphic disorder (BDD), a mental disorder in which one is extremely critical of his or her physique or self-image to an obsessive and compulsive degree.  As it is with anorexia, a person with BDD is said to show signs of a characteristic called distorted body image. In layman's terms, anorexia sufferers commonly believe they are overweight, many times claiming they see themselves as "fat," when in reality, they are nutritionally underweight and physically much thinner than the average person.  In the same way, a sufferer of "tanorexia" may believe him or herself to have a much lighter--even a pale--complexion when he or she is actually quite dark-skinned.

## Symptoms of tanorexia
Although the syndrome has not been officially described by the medical community, reported symptoms may include: intense anxiety if a session of tanning is missed, competition among peers to see which can get the darkest tan, and chronic frustration about the color of one's skin, with the affected person being convinced his or her complexion is constantly lighter than it actually is.