Smoking, especially heavy smoking, is an important predisposing factor but the reasons for this relationship are unknown. One hypothesis is that cigarette smoke contains nutritional factors for "C. albicans", or that local epithelial alterations occur that facilitate colonization of candida species.

Malnutrition, whether by malabsorption, or poor diet, especially hematinic deficiencies (iron, vitamin B12, folic acid) can predispose to oral candidiasis, by causing diminished host defense and epithelial integrity. For example, iron deficiency anemia is thought to cause depressed cell-mediated immunity. Some sources state that deficiencies of vitamin A or pyridoxine are also linked.

There is limited evidence that a diet high in carbohydrates predisposes to oral candidiasis. "In vitro" and studies show that Candidal growth, adhesion and biofilm formation is enhanced by the presence of carbohydrates such as glucose, galactose and sucrose.

A 2003 survey of diseases of the foot in 16 European countries found onychomycosis to be the most frequent fungal foot infection and estimates its prevalence at 27%. Prevalence was observed to increase with age. In Canada, the prevalence was estimated to be 6.48%. Onychomycosis affects approximately one-third of diabetics and is 56% more frequent in people suffering from psoriasis.

A diet that supports the immune system and is not high in simple carbohydrates contributes to a healthy balance of the oral and intestinal flora. While yeast infections are associated with diabetes, the level of blood sugar control may not affect the risk. Wearing cotton underwear may help to reduce the risk of developing skin and vaginal yeast infections, along with not wearing wet clothes for long periods of time.

Oral hygiene can help prevent oral candidiasis when people have a weakened immune system. For people undergoing cancer treatment, chlorhexidine mouthwash can prevent or reduce thrush. People who use inhaled corticosteroids can reduce the risk of developing oral candidiasis by rinsing the mouth with water or mouthwash after using the inhaler.

For women who experience recurrent yeast infections, there is limited evidence that oral or intravaginal probiotics help to prevent future infections. This includes either as pills or as yogurt.

Among individuals being treated in intensive care units, the mortality rate is about 30-50% when systemic candidiasis develops.

Several drugs may cause AC as a side effect, by various mechanisms, such as creating drug-induced xerostomia. Various examples include isotretinoin, indinavir, and sorafenib. Isotretinoin (Accutane), an analog of vitamin A, is a medication which dries the skin. Less commonly, angular cheilitis is associated with primary hypervitaminosis A, which can occur when large amounts of liver (including cod liver oil and other fish oils) are regularly consumed or as a result from an excess intake of vitamin A in the form of vitamin supplements. Recreational drug users may develop AC. Examples include cocaine, methamphetamines, heroin, and hallucinogens.

Following effective treatment recurrence is common (10–50%).

Nail fungus can be painful and cause permanent damage to nails. It may lead to other serious infections if the immune system is suppressed due to medication, diabetes or other conditions. The risk is most serious for people with diabetes and with immune systems weakened by leukemia or AIDS, or medication after organ transplant. Diabetics have vascular and nerve impairment, and are at risk of cellulitis, a potentially serious bacterial infection; any relatively minor injury to feet, including a nail fungal infection, can lead to more serious complications. Infection of the bone is another rare complication.

Tobacco smoking or chewing is the most common causative factor, with more than 80% of persons with leukoplakia having a positive smoking history. Smokers are much more likely to suffer from leukoplakia than non-smokers. The size and number of leukoplakia lesions in an individual is also correlated with the level of smoking and how long the habit has lasted for. Other sources argue that there is no evidence for a direct causative link between smoking and oral leukoplakia. Cigarette smoking may produce a diffuse leukoplakia of the buccal mucosa, lips, tongue and rarely the floor of mouth. Reverse smoking, where the lit end of the cigarette is held in the mouth is also associated with mucosal changes. Tobacco chewing, e.g. betel leaf and areca nut, called paan, tends to produce a distinctive white patch in a buccal sulcus termed "tobacco pouch keratosis". In the majority of persons, cessation triggers shrinkage or disappearance of the lesion, usually within the first year after stopping.

Acute paronychia is usually caused by bacteria. Claims have also been made that the popular acne medication, isotretinoin, has caused paronychia to develop in patients. Paronychia is often treated with antibiotics, either topical or oral. Chronic paronychia is most often caused by a yeast infection of the soft tissues around the nail but can also be traced to a bacterial infection. If the infection is continuous, the cause is often fungal and needs antifungal cream or paint to be treated.

Risk factors include repeatedly washing hands and trauma to the cuticle such as may occur from biting. In the context of bartending, it is known as "bar rot".

Prosector's paronychia is a primary inoculation of tuberculosis of the skin and nails, named after its association with prosectors, who prepare specimens for dissection. Paronychia around the entire nail is sometimes referred to as "runaround paronychia".

Painful paronychia in association with a scaly, erythematous, keratotic rash (papules and plaques) of the ears, nose, fingers, and toes may be indicative of acrokeratosis paraneoplastica, which is associated with squamous cell carcinoma of the larynx.

Paronychia can occur with diabetes, drug-induced immunosuppression, or systemic diseases such as pemphigus.

Some systemic disorders are involved in angular cheilitis by virtue of their association with malabsorption and the creation of nutritional deficiencies described above. Such examples include people with anorexia nervosa. Other disorders may cause lip enlargement (e.g. orofacial granulomatosis), which alters the local anatomy and extenuates the skin folds at the corners of the mouth. More still may be involved because they affect the immune system, allowing normally harmless organisms like Candida to become pathogenic and cause an infection. Xerostomia (dry mouth) is thought to account for about 5% of cases of AC. Xerostomia itself has many possible causes, but commonly the cause may be side effects of medications, or conditions such as Sjögren's syndrome. Conversely, conditions which cause drooling or sialorrhoea (excessive salivation) can cause angular cheilitis by creating a constant wet environment in the corners of the mouth. About 25% of people with Down syndrome appear to have AC. This is due to relative macroglossia, an apparently large tongue in a small mouth, which may constantly stick out of the mouth causing maceration of the corners of the mouth with saliva. Inflammatory bowel diseases (such as Crohn's disease or ulcerative colitis) can be associated with angular cheilitis. In Crohn's, it is likely the result of malabsorption and immunosuppressive therapy which gives rise to the sores at the corner of the mouth. Glucagonomas are rare pancreatic endocrine tumors which secrete glucagon, and cause a syndrome of dermatitis, glucose intolerance, weight loss and anemia. AC is a common feature of glucagonoma syndrome. Infrequently, angular cheilitis may be one of the manifestations of chronic mucocutaneous candidiasis, and sometimes cases of oropharyngeal or esophageal candidiasis may accompany angular cheilitis. Angular cheilitis may be present in human immunodeficiency virus infection, neutropenia, or diabetes. Angular cheilitis is more common in people with eczema because their skin is more sensitive to irritants. Other conditions possibly associated include plasma cell gingivitis, Melkersson-Rosenthal syndrome, or sideropenic dysphagia (also called Plummer-Vinson syndrome or Paterson-Brown-Kelly syndrome).

Although the synergistic effect of alcohol with smoking in the development of oral cancer is beyond doubt, there is no clear evidence that alcohol is involved in the development of leukoplakia, but it does appear to have some influence. Excessive use of a high alcohol containing mouth wash (> 25%) may cause a grey plaque to form on the buccal mucosa, but these lesions are not considered true leukoplakia.

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.

Candidal intertrigo is an infection of the skin by "Candida albicans", more specifically located between intertriginous folds of adjacent skin.

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.

This is a rare inflammatory condition of the minor salivary glands, usually in the lower lip, which appears swollen and everted. There may also be ulceration, crusting, abscesses, and sinus tracts. It is an acquired disorder, but the cause is uncertain. Suspected causes include sunlight, tobacco, syphilis, poor oral hygiene and genetic factors. The openings of the minor salivary gland ducts become inflamed and dilated, and there may be mucopurulent discharge from the ducts. A previous classification suggested dividing cheilitis into 3 types based on severity, with the later stages involving secondary infection with bacteria, and increased ulceration, suppuration and swelling: Type 1, Simple; Type 2, Superficial suppurative ("Baelz's disease"); and Type 3, Deep suppurative ("cheilitis glandularis epostemetosa"). Cheilitis glandularis usually occurs in middle-aged and elderly males, and it carries a risk of malignant transformation to squamous cell carcinoma (18% to 35%). Preventative treatment such as vermilionectomy ("lip shave") is therefore the treatment of choice.

Paronychia may be divided as follows:

- "Acute paronychia" is an infection of the folds of tissue surrounding the nail of a finger or, less commonly, a toe, lasting less than six weeks. The infection generally starts in the paronychium at the side of the nail, with local redness, swelling, and pain. Acute paronychia is usually caused by direct or indirect trauma to the cuticle or nail fold, and may be from relatively minor events, such as dishwashing, an injury from a splinter or thorn, nail biting, biting or picking at a hangnail, finger sucking, an ingrown nail, or manicure procedures.

- "Chronic paronychia" is an infection of the folds of tissue surrounding the nail of a finger or, less commonly, a toe, lasting more than six weeks. It is a nail disease prevalent in individuals whose hands or feet are subject to moist local environments, and is often due to contact dermatitis. In chronic paronychia, the cuticle separates from the nail plate, leaving the region between the proximal nail fold and the nail plate vulnerable to infection. It can be the result of dish washing, finger sucking, aggressively trimming the cuticles, or frequent contact with chemicals (mild alkalis, acids, etc.).

Alternatively, paronychia may be divided as follows:

- "Candidal paronychia" is an inflammation of the nail fold produced by "Candida albicans".

- "Pyogenic paronychia" is an inflammation of the folds of skin surrounding the nail caused by bacteria. Generally acute paronychia is a pyogenic paronychia as it is usually caused by a bacterial infection.

Opportunistic infections (infections that are caused by a diminished immune system) are frequent. Fungus from an athlete's foot infection can spread to the groin through clothing. Tight, restrictive clothing, such as jockstraps, traps heat and moisture, providing an ideal environment for the fungus.

The type of fungus involved is usually "Trichophyton rubrum". Some other contributing fungi are "Candida albicans", "Trichophyton mentagrophytes" and "Epidermophyton floccosum".

Bacterial intertrigo can be caused by "Streptococci" and "Corynebacterium minutissimum".

An intertrigo usually develops from the chafing of warm, moist skin in the areas of the inner thighs and genitalia, the armpits, under the breasts, the underside of the belly, behind the ears, and the web spaces between the toes and fingers. An intertrigo usually appears red and raw-looking, and may also itch, ooze, and be sore. Intertrigos occur more often among overweight individuals, those with diabetes, those restricted to bed rest or diaper use, and those who use medical devices, like artificial limbs, that trap moisture against the skin. Also, there are several skin diseases that can cause an intertrigo to develop, such as dermatitis or inverse psoriasis.

Periungual warts are warts that cluster around the fingernail or toenail. They appear as thickened, fissured cauliflower-like skin around the nail plate. Periungual warts often cause loss of the cuticle and paronychia. Nail biting increases susceptibility to these warts.

Warts of this kind often cause damage to the nail either by lifting the nail from the skin or causing the nail to partially detach. If they extend under the nail, then the patient may suffer pain as a result. Sometimes periungual wart infections resemble the changes that are found in onychomycosis. In worst cases, if the infection causes injury or damage to the nail matrix, deformity in the nail may become permanent.

As with other wart types, a number of treatments are available, including laser therapy, cryotherapy, salicylic acid, and other topical treatments.

Tinea cruris is similar to, but different from Candidal intertrigo, which is an infection of the skin by "Candida albicans". The latter is more specifically located between intertriginous folds of adjacent skin, which can be present in the groin or scrotum, and be indistinguishable from fungal infections caused by "tinea". However, candidal infections tend to both appear and with treatment disappear more quickly. It may also affect the scrotum.

Also termed "cheilitis exfoliativa" or "tic de levres", is an uncommon inflammatory condition of the vermilion zone of the lips, which are painful and crusted. There is continuous production and desquamation (shedding) of thick, brown scales of keratin. The keratin layer of the epidermis of the lips experiences a faster growth and death rate than normal and desquamates. When these scales are removed, a normal appearing lip is revealed beneath, although there may be associated erythema and edema. The condition has not yet been attributed to any particular cause. Rarely are infections to blame. In some individuals, there is an association with stress, anxiety, depression or personality disorders. In one report, 87% of individuals had some form of psychiatric disturbance, and 47% had thyroid dysfunction, which in turn can cause psychiatric conditions like depression.

Some cases of exfoliative cheilitis are thought to represent factitious damage, termed "factitious cheilitis" or "artifactual cheilitis", and are related to repetitive lip picking or licking habits. This appears as crusting and ulceration caused by repetitive chewing and sucking of the lips. Some consider habitual lip licking or picking to be a form of nervous tic. This habit is sometimes termed "perlèche" (derived from the French word "pourlècher" meaning "to lick one’s lips"). Factitious cheilitis is significantly more common in young females.

Exfoliative cheilitis has also been linked to HIV/AIDS. Management consists mostly of keeping the lips moist and the application of topical corticosteroids ranging from hydrocortisone to clobetasol. There have also been reports of using topical tacrolimus ointment.

Patients with the following conditions, treatments or situations are at increased risk for invasive candidiasis.

- Critical illness

- Long-term intensive care unit stay

- Abdominal surgery (aggravated by anastomotic leakage or repeat laparotomies)

- Immunosuppressive diseases

- Acute necrotizing pancreatitis

- Malignant hematologic disease

- Solid-organ transplantation

- Hematopoietic stem cell transplantation

- Solid-organ tumors

- Neonates (especially low birth weight and preterm infants)

- Broad-spectrum antibiotic treatment

- Central venous catheter

- Internal prosthetic device

- Total parenteral nutrition

- Hemodialysis

- Glucocorticoid use

- Chemotherapy

- Noninvasive "Candida" colonization (particularly if multifocal)

Hangnails can become infected and cause paronychia, a type of skin infection that occurs around the nails. Treatments for paronychia vary with severity, but may include soaking in hot salty water, the use of oral antibiotic medication, or clinical lancing. Paronychia itself rarely results in further complications but can lead to abscess, permanent changes to the shape of the nail or the spread of infection.

Candidal onychomycosis is an infection of the nail plate by fungus caused by "Candida". In one study "Candida parapsilosis" was the most common species; "Candida albicans" is also a common agent.