Recurrent miscarriage in itself is associated with later development of coronary artery disease with an odds ratio of approximately 2, increased risk of ovarian cancer, increased risk of cardiovascular complications, and an increased risk of all-cause mortality of 44%, 86%, and 150% for women with a history of 1, 2, or 3 miscarriages, respectively.

Women with a history of recurrent miscarriage are at risk of developing preeclampsia in later pregnancies.

Not only is obesity associated with miscarriage, it can result in sub-fertility and other adverse pregnancy outcomes. Recurrent miscarriage is also related to obesity. Women with bulimia nervosa and anorexia nervosa may have a greater risk for miscarriage. Nutrient deficiencies have not been found to impact miscarriage rates but hyperemesis gravidarum sometimes precedes a miscarriage.

Caffeine consumption also has been correlated to miscarriage rates, at least at higher levels of intake. However, such higher rates have been found to be statistically significant only in certain circumstances.

Vitamin supplementation has generally not shown to be effective in preventing miscarriage. Chinese traditional medicine has not been found to prevent miscarriage.

Immunization of mothers against male-specific minor histocompatibility (H-Y) antigens has a pathogenic role in many cases of "secondary recurrent miscarriage", that is, recurrent miscarriage in pregnancies succeeding a previous live birth. An example of this effect is that the male:female ratio of children born prior and subsequent to secondary recurrent miscarriage is 1.49 and 0.76 respectively.

Several intercurrent diseases in pregnancy can potentially increase the risk of miscarriage, including diabetes, polycystic ovary syndrome (PCOS), hypothyroidism, certain infectious diseases, and autoimmune diseases. PCOS may increases the risk of miscarriage. Two studies suggested treatment with the drug metformin significantly lowers the rate of miscarriage in women with PCOS, but the quality of these studies has been questioned. The use metformin treatment in pregnancy has not been shown to be safe. In 2007 the Royal College of Obstetricians and Gynaecologists also recommended against use of the drug to prevent miscarriage. Thrombophilias or defects in coagulation and bleeding were once thought to be a risk in miscarriage but have been subsequently questioned.

Severe cases of hypothyroidism increase the risk of miscarriage. The effect of milder cases of hypothyroidism on miscarriage rates has not been established. A condition called luteal phase defect (LPD) is a failure of the uterine lining to be fully prepared for pregnancy. This can keep a fertilized egg from implanting or result in miscarriage.

"Mycoplasma genitalium" infection is associated with increased risk of preterm birth and miscarriage.

Infections can increase the risk of a miscarriage: rubella (German measles), cytomegalovirus, bacterial vaginosis, HIV, chlamydia, gonorrhoea, syphilis, and malaria.

Most studies of uterine malformations are based on populations of women who have experienced a pregnancy loss and thus do not address the issue of the prevalence in the general population. A screening study by Woelfer et al. of women without a history of reproductive problems found that about 5% of women had an arcuate uterus when they defined an arcuate uterus any fundal protrusion into the cavity that had an apical angle of more than 90 degrees. Accordingly, it was the most common uterine anomaly, followed by septate uterus (3%) and bicornuate uterus (0.5%).

The condition may not be known to the affected individual and not result in any reproductive problems; thus normal pregnancies occur. Indeed, there is no consensus on the relationship of the arcuate uterus and recurrent pregnancy loss. Accordingly, the condition may be a variation or a pathology.

One view maintains that the condition is associated with a higher risk for miscarriage, premature birth, and malpresentation. Thus a study that evaluated women with uterine bleeding by hysteroscopy found that 6.5% of subjects displayed the arcuate uterus and had evidence of reproductive impairments. A study based on hysterosalpingraphic detected arcuate lesions documented increased fetal loss and obstetrical complications as a risk for affected women. Woelfer found that the miscarriage risk is more pronounced in the second trimester. In contrast, a study utilizing 3-D ultrasonography to document the prevalence of the arcuate uterus in a gynecological population found no evidence of increased risk of reproductive loss; in this study 3.1% of women had an arcuate uterus making it the most common uterine anomaly; this prevalence was similar than in women undergoing sterilization and lower than in women with recurrent pregnancy loss.

It is generally treated surgically, with a hymenotomy or other surgery to remove any tissue that blocks the menstrual flow.

Histomorphologically, VUE is characterized by a lymphocytic infiltrate of the chorionic villi without a demonstrable cause. Plasma cells should be absent; the presence of plasma cells suggests an infective etiology, e.g. CMV infection.

Villitis of unknown etiology, abbreviated VUE, is an inflammatory process that involves the chorionic villi (villitis) whose cause (etiology) is not known. VUE is associated with recurrent miscarriage and intrauterine growth restriction, and recurs in subsequent pregnancies.

Hematocolpos is a medical condition in which the vagina fills with menstrual blood. It is often caused by the combination of menstruation with an imperforate hymen. It is sometimes seen in Robinow syndrome, uterus didelphys, or other congenital conditions.

A related disorder is hematometra, where the uterus fills with menstrual blood. It presents after puberty as primary amenorrhoea, recurrent pelvic pain with a pelvic mass. This can be caused by a congenital stenosis of the cervix, or by a complication of a surgical treatment.

While infections may occur without sex, a high frequency of intercourse increases the risk. Personal hygiene methods or tight-fitting clothing, such as tights and thong underwear, do not appear to increase the risk.

In pregnancy, higher levels of estrogen make a woman more likely to develop a yeast infection. During pregnancy, the "Candida" fungus is more common, and recurrent infection is also more likely. There is tentative evidence that treatment of asymptomatic candidal vulvovaginitis in pregnancy reduces the risk of preterm birth.

Little is known about the cause of vestibulodynia. A number of causes may be involved, including sub-clinical human papillomavirus infection, chronic recurrent candidiasis, or chronic recurrent bacterial vaginosis. Muscular causes have been implicated as well, since chronic vulvar pain may be the result of chronic hypertonic perivaginal muscles, leading to vaginal tightening and subsequent pain. Some investigators have postulated the existence of neurological causes, such as vestibular neural hyperplasia. Finally, psychological factors may contribute to or exacerbate the problem, since the anticipation of pain often results in a conditioned spasmodic reflex along with sexual desire and arousal problems.

Urethrorrhagia refers to urethral bleeding in the absence of urine associated with dysuria and blood spots on underwear after voiding. This condition, which often occurs in prepubertal boys at intervals several months apart over a period of many years, has a benign self-limited course. Radiological studies as well as endoscopic procedures are unnecessary in the early management of these patients thus being relegated to recurrent or persistent bleeding.

Congenital disorder of glycosylation type IIc or Leukocyte adhesion deficiency-2 (LAD2) is a type of leukocyte adhesion deficiency attributable to the absence of neutrophil sialyl-LewisX, a ligand of P- and E-selectin on vascular endothelium. It is associated with "SLC35C1".

This disorder was discovered in two unrelated Israeli boys 3 and 5 years of age, each the offspring of consanguineous parents. Both had severe mental retardation, short stature, a distinctive facial appearance, and the Bombay (hh) blood phenotype, and both were secretor- and Lewis-negative. They both had had recurrent severe bacterial infections similar to those seen in patients with LAD1, including pneumonia, peridontitis, otitis media, and localized cellulitis. Similar to that in patients with LAD1, their infections were accompanied by pronounced leukocytosis (30,000 to 150,000/mm) but an absence of pus formation at sites of recurrent cellulitis. In vitro studies revealed a pronounced defect in neutrophil motility. Because the genes for the red blood cell H antigen and for the secretor status encode for distinct α1,2-fucosyltransferases and the synthesis of Sialyl-LewisX requires an α1,3-fucosyltransferase, it was postulated that a general defect in fucose metabolism is the basis for this disorder. It was subsequently found that GDP-L-fucose transport into Golgi vesicles was specifically impaired, and then missense mutations in the GDP-fucose transporter cDNA of three patients with LAD2 were discovered. Thus, GDP-fucose transporter deficiency is a cause of LAD2.

Diagnosis is readily made by the cotton-swab test, in which pressure is applied in a circular fashion around the vulvar vestibule to assess complaints of pain. Laboratory tests are used to exclude bacterial or viral infection, and a careful examination of the vulvo/vaginal area is conducted to assess whether any atrophy is present.

Children with DOCK8 deficiency do not tend to live long; sepsis is a common cause of death at a young age. CNS and vascular complications are other common causes of death.

DOCK8 deficiency is very rare, estimated to be found in less than one person per million; there have been 32 patients diagnosed as of 2012.

CRMO was once considered strictly a childhood disease, but adults have been diagnosed with it. The affected tends to range from 4 to 14 years old, with 10 as the median age. As stated above, CRMO occurs 1:1,000,000 and primarily in girls with a 5:1 ratio. That means out of six million, there will probably be 5 girls and 1 boy with the condition.

Some malignancies, especially gliomas (25%), as well as adenocarcinomas of the pancreas and lung, are associated with hypercoagulability (the tendency to form blood clots) for reasons that are incompletely understood, but may be related to factors secreted by the tumors, in particular a circulating pool of cell-derived tissue factor-containing microvesicles. Some adenocarcinomas secrete mucin that can interact with selectin found on platelets, thereby causing small clots to form.

In patients with malignancy-associated hypercoagulable states, the blood may spontaneously form clots in the portal vessels, the deep veins of the extremities (such as the leg), or the superficial veins anywhere on the body. These clots present as visibly swollen blood vessels (thrombophlebitis), especially the veins, or as intermittent pain in the affected areas.

MCAS is a relatively new diagnosis, being unnamed until 2007, and is believed to be very under-diagnosed. New findings are revealing that MCAS is much more prevalent than previously thought.

The thickness of the mucosa may be an important factor in aphthous stomatitis. Usually, ulcers form on the thinner, non-keratinizing mucosal surfaces in the mouth. Factors which decrease the thickness of mucosa increase the frequency of occurrence, and factors which increase the thickness of the mucosa correlate with decreased ulceration.

The nutritional deficiencies associated with aphthous stomatitis (B12, folate, and iron) can all cause a decrease in the thickness of the oral mucosa (atrophy).

Local trauma is also associated with aphthous stomatitis, and it is known that trauma can decrease the mucosal barrier. Trauma could occur during injections of local anesthetic in the mouth, or otherwise during dental treatments, frictional trauma from a sharp surface in the mouth such as broken tooth, or from tooth brushing.

Hormonal factors are capable of altering the mucosal barrier. In one study, a small group of females with apthous stomatitis had fewer occurrences of aphthous ulcers during the luteal phase of the menstrual cycle or with use of the contraceptive pill. This phase is associated with a fall in progestogen levels, mucosal proliferation and keratinization. This subgroup often experiences remission during pregnancy. However, other studies report no correlation between aphthous stomatitis and menstrual period, pregnancy or menopause.

Aphthous stomatitis is common in people who smoke, and there is also a correlation between habit duration and severity of the condition. Tobacco use is associated with an increase in keratinization of the oral mucosa. In extreme forms, this may manifest as leukoplakia or stomatitis nicotina (smoker's keratosis). This increased keratinization may mechanically reinforce the mucosa and reduce the tendency of ulcers to form after minor trauma, or present a more substantial barrier to microbes and antigens, but this is unclear. Nicotine is also known to stimulate production of adrenal steroids and reduce production of TNF-α, interleukin-1 and interleukin-6. Smokeless tobacco products also seem to protect against aphthous stomatitis. Cessation of smoking is known to sometimes precede the onset of aphthous stomatitis in people previously unaffected, or exacerbate the condition in those who were already experiencing aphthous ulceration. Despite this correlation, starting smoking again does not usually lessen the condition.

Several aetiologies are suggested, and any combination of these may be present in any given case.

- Vitamin deficiency (A, B or C)

- Viral infection

- Bacterial infection

- "Leptospira

- "Streptococcus

- "Brucella

- Parasitic infection

- Strongyle

- "Onchocerca cervicalis"

- Autoimmune disease

The disease has been suggested to be primarily autoimmune in nature, being a delayed hypersensitivity reaction to any of the above agents.

Over time, the relapse rate is high, exceeding 50%. However, recent research indicates that combination therapies offer a better prognosis than antibiotics alone.

A 2007 study showed that repeated combination pharmacological therapy with antibacterial agents (ciprofloxacin/azithromycin), alpha-blockers (alfuzosin) and Serenoa repens extracts may eradicate infection in 83.9% of patients with clinical remission extending throughout a follow-up period of 30 months for 94% of these patients.

A 2014 study of 210 patients randomized into two treatment groups found that recurrence occurred within 2 months in 27.6% of the group using antibiotics alone (prulifloxacin 600 mg), but in only 7.8% of the group taking prulifloxacin in combination with Serenoa repens extract, Lactobacillus Sporogens and Arbutin.

People with recurrent boils are as well more likely to have a positive family history, take antibiotics, and to have been hospitalised, anemic, or diabetic; they are also more likely to have associated skin diseases and multiple lesions.