Brain-derived neurotrophic factor (BDNF) is under investigation as a possible mechanism.There is evidence that sex hormones may influence appetite and eating in women and the onset of bulimia nervosa. Studies have shown that women with hyperandrogenism and polycystic ovary syndrome have a dysregulation of appetite, along with carbohydrates and fats. This dysregulation of appetite is also seen in women with bulimia nervosa. In addition, gene knockout studies in mice have shown that mice that have the gene encoding estrogen receptors have decreased fertility due to ovarian dysfunction and dysregulation of androgen receptors. In humans, there is evidence that there is an association between polymorphisms in the ERβ (estrogen receptor β) and bulimia, suggesting there is a correlation between sex hormones and bulimia nervosa.Bulimia has been compared to drug addiction, though the empirical support for this characterization is limited. However, people with bulimia nervosa may share dopamine D2 receptor-related vulnerabilities with those with substance use disorders.Dieting, a common behaviour in bulimics, is associated with lower plasma tryptophan levels. Decreased tryptophan levels in the brain, and thus the synthesis of serotonin, such as via acute tryptophan depletion, increases bulimic urges in currently and formerly bulimic individuals within hours.Abnormal blood levels of peptides important for the regulation of appetite and energy balance are observed in individuals with bulimia nervosa, but it remains unknown if this is a state or trait.In recent years, evolutionary psychiatry as an emerging scientific discipline has been studying mental disorders from an evolutionary perspective.
A stye, also known as a hordeolum, is a bacterial infection of an oil gland in the eyelid. This results in a red tender bump at the edge of the eyelid. The outside or the inside of the eyelid can be affected.The cause of a stye is usually a bacterial infection by Staphylococcus aureus. The internal ones are due to infection of the meibomian gland while the external ones are due to an infection of the gland of Zeis. A chalazion on the other hand is a blocked oil gland without infection. A chalazion is typically in the middle of the eyelid and not painful.Often a stye will go away without any specific treatment in a few days or weeks. Recommendations to speed improvement include warm compresses. Occasionally antibiotic eye ointment may be recommended. While these measures are often recommended, there is little evidence for use in internal styes. The frequency at which styes occur is unclear, though they may occur at any age. Signs and symptoms
The first sign of a stye is a small, yellowish spot at the center of the bump that develops as pus and expands in the area.Other stye symptoms may include:

A lump on the top or bottom eyelid
Localized swelling of the eyelid
Localized pain
Redness
Tenderness
Crusting of the eyelid margins
Burning in the eye
Droopiness of the eyelid
Scratchy sensation on the eyeball (itching)
Blurred vision
Mucous discharge in the eye
Irritation of the eye
Light sensitivity
Tearing
Discomfort during blinking
Sensation of a foreign body in the eye

Complications
Stye complications occur in very rare cases.