Differently from other microbes, the mere isolation of Candida from intraoral surfaces is not interpreted as a predictive signal for disease. The commensal status of such fungal genus has been evaluated along the years and according to different authors, 54–71.4 % of healthy individuals from diverse populations may carry such yeasts without any symptom (Hauman et al. 1993; Darwazeh and al-Bashir 1995; Kindelan et al. 1998; Blignaut et al. 2002). Although high counts of yeast cells in saliva may be interpreted as a suggestive signal of candidosis, not always it will occur. Akpan and Morgan (2002) have compiled data concerning to carrier status of individuals from different risk groups and stated that in the general population, carriage rates have been reported to range from 20 to 75 % without any symptoms. According to them, the incidence of Candida isolated from the oral cavity (not related to OC episodes) has been reported to be 45 % in neonates, 45–65 % of healthy children, 30–45 % of healthy adults, 50–65 % of people who wear removable dentures, 65–88 % in those residing in acute and long-term care facilities, 90 % of patients with acute leukemia undergoing chemotherapy, and 95 % of patients with HIV.

Albeit the above statement, OC occurs when some predisposing conditions favor the fungal pathogenic shift.

Regarding to age, there is a medical maxim that says “oral thrush (syn. pseudomembranous candidosis, moniliasis) is common in the very young, the very old, or the very sick”.

Oral thrush is a disease affecting around 1 in 20 babies. The Centers for Disease Control and Prevention estimates that OC is seen in between 5 and 7 % of babies less than 1 month old (CDC 2013). Premature babies (born before 37 weeks) have an increased risk of developing oral thrush. There is a consensus among pediatricians and pediatric dentists that oral thrush may occur in infants up to 2 years old.

People belonging to the second group in the aphorism (very old people) are more prone to develop OC due to their compromised health conditions and, for a great group of them, to the fact that they wear dentures. Elderly, almost always, implies in a diminishing of immune status with age-related high expression of TGF-β and low elastase and salivary peroxidase activities. Also, negative modulating receptors expression on salivary neutrophils may occur (Gasparoto et al., 2012). Add to that, the fact that elder people experience a decrease and a functional impairment in the population of circulating T cells (Girard et al., 1977).

Other comorbidities and conditions typical of such population as diabetes, hypertension, dehydration, undernutrition, and medicine intake to treat anxiety or depression lead to severe reductions in the salivary production, incurring in high predisposition to convert saprophytic yeasts into opportunistic pathogens.

Epidemiological data show that 65–84.1 % of elder denture wearers may harbor Candida spp. in their mouths (Budtz-Jorgensen et al., 1975; de Resende et al., 2006). Dentures per se constitute a predisposing factor for candidosis, once the acrylic surfaces act as a fungal reservoir. Also, broken and loosely adapted dentures may cause attrition-related lesions in which the fungus develops more promptly.

The deleterious habit of cigarette smoking is clearly recognized as a predisposing factor for OC, and the heavy cigarette consumption are associated with predisposition to some complications. The smoking habit may provoke increased oral epithelial keratinization and subsequent enhancement of hydrophobicity, which may predispose the smoker to higher oral yeast colonization (Williams et al., 1999).

It was demonstrated that constituents of cigarette smoke may increase fungal virulence attributes (Baboni et al., 2009, 2010). Soysa and Ellepola (2005) compiled data from various studies and stated that cigarette smoking provokes increments in oral candidal carriage in smokers. Complications like candidal leukoplakia (Arendorf et al., 1983; Daftary et al., 1972) are more commonly found occurring in smokers than in nonsmokers. Chronic hyperplastic candidosis can be solved by suppressing tobacco consumption (Holmstrup and Bessermann 1983).

The reduction in salivary flow rate is universally considered as one of the most important predisposing factor for oral candidal increments and candidosis. Some conditions can determine or contribute to such events. Salivary gland hypofunction may be a result of (i) enhanced sympathetic drive during prolonged anxiety events; (ii) age-related dehydration, diabetes, or inaccessibility to water; (iii) isolated or polypharmacy iatrogenic action of anticholinergics (atropine, atropinics, and hyoscine), central-acting psychoactive agents (antidepressants, phenothiazines, benzodiazepines, and antihistamines), drugs acting on sympathetic system (sympathomimetics, alpha-1 antagonists, alfa-2 agonists and beta-blockers), cytotoxic drugs, diuretics, opioids, methamphetamine, heroin, and correlates, among other medicines and illegal drugs; (iv) prolonged diarrhea; (v) renal failure; and (vi) Sjögren’s syndrome; (vii) radiotherapy to treat head/neck cancer; among others.

As this condition may be caused by numberless etiologic factors, the epidemiology of hyposalivation-related OC is somehow difficult to be established. Among people suffering from Sjögren’s syndrome, OC may achieve 87 % of patients (Yan et al., 2011). It has been reported that 55.2 % of patients with cancer in the head/neck region who were in a radiotherapy regimen experienced OC during the course of the treatment (Deng et al., 2010).

Besides periodontal diseases and caries, the negligence in oral cleansing also can drive to candidosis. This negligence is especially markedly in some risk groups as elders, drug addicts, and hospitalized patients.

Despite the increase in predisposition to OC in denture wearers, per se, factors as educational status, level of income, dental visiting frequency, denture conditions, brushing methods, and brushing frequency are determinants of OC. Positive relationships can be observed between poor denture hygiene habits and denture-related stomatitis, in up to 44 % of patients (Evren et al., 2011). Some patients merely wash their prosthesis with water or just with a toothbrush.

According to the Recovery Organization, an estimated 40–60 % of those addicted to drugs face addiction relapse (Recovery.org 2013). The low self-esteem led such individuals to neglect their appearance and hygiene. It has been demonstrated that 10.9 % of polydrug users attended in a specialized clinic in Madrid, Spain, presented angular cheilitis (Mateos-Moreno et al., 2013), a condition commonly found in people with nutritional deficiencies (especially, folate, iron, or vitamin B2), poorly maintained dentures, or immunosuppression.

Poor oral hygiene also is critical for hospitalized patients. A survey conducted in a Brazilian hospital revealed that oral hygiene is more commonly associated to age than to physical disability (Carrilho Neto et al., 2011). Involved investigators reported that 69 % of patients presented poor oral hygiene and 19.6 % presented OC. Some other complications as coma (Cecon et al., 2010), cancer (Meurman and Gronroos 2010; Davies et al., 2008), dentures (Tosello et al., 2008), or immunosuppression (Palmason et al., 2011) tend to increase the possibility of institutionalized patients to develop OC.

People suffering from central nervous system diseases, mainly those receiving heavy psychotropic medications with anticholinergic effects, are more prone to experience OC once hyposalivation may occur as a result of the burden of combined drugs as chlorpromazine, benztropine, lithium, and risperidone (Stevens 2007). In some cases, patients with deep nervous disorders (e.g., dementia) require accessory treatment to attenuate OC that occurs (Lloyd-Williams 1996).

Other group of patients that requires special dedicated attention is the terminally ill patients. OC is common in advanced cancer cases occurring in 31–70 % or 83 % of patients and clearly affecting the quality of their remaining life (Aldred et al., 1991; Ball et al., 1998; Butticaz et al., 2003). As most of those patients are aged and wear dentures, a high proportion of them present diverse variants of OC, including angular cheilitis (Chaushu et al., 2000). Molecular methods based on fungal DNA fingerprinting revealed that antifungal treatment in this patient group fails to eradicate the original Candida sp. strain, thereby allowing recolonization of the oral cavity (Wilson et al., 2001).

There are no doubts that the most well-known predisposing factor to OC is the immunosuppressant effect of human immunodeficiency virus (HIV) in AIDS patients.

Before the advent of the highly active antiretroviral therapy (HAART) era in 2000–2001, oral candidoses were common comorbidities occurring in a variable range of 50–52 % (Schulten et al., 1989; Morace et al., 1990; Ramirez et al., 1990) to 94 % (Tukutuku et al., 1990) of HIV-infected individuals. HAART has produced an impressive decline in the incidence of opportunistic infections in HIV-infected adults and children becoming uncommon. In certain cases, such prevalence has dropped to as low values as 1.87 % (Gona et al., 2006). However, in some localities, the addicts’ ignorance or the inaccessibility to medication imply high casuistic of OC (Solomon et al., 2008; Evans et al., 2012; Pattrapornnan and Derouen 2013; Zhang et al., 2009) even in industrialized countries (Tappuni and Fleming 2001; Tami-Maury et al. 2011).

A particular predisposing factor for OC is diabetes mellitus. It is estimated that 15.1 % of insulin-dependent diabetes mellitus (IDDM) (Guggenheimer et al., 2000) and 24 % of type-2 diabetes are prone to OC (Bajaj et al., 2012). Indeed, the diabetic patient presents various predisposing conditions that corroborate to OC occurring as hyposalivation, impaired local immune response, higher salivary glucose concentration; many of them wear dentures, etc.

Of significant importance, literature reveals that there is a significant higher obtaining of Candida albicans than other Candida spp. in positive oral harvestings. Such result is perceptible in both healthy carriers and ill individuals (Obladen 2012; Calcaterra et al., 2013; Castro et al., 2013