Tinea corporis is caused by a tiny fungus known as dermatophyte. These tiny organisms normally live on the superficial skin surface, and when the opportunity is right, they can induce a rash or infection.

The disease can also be acquired by person-to-person transfer usually via direct skin contact with an infected individual. Animal-to-human transmission is also common. Ringworm commonly occurs on pets (dogs, cats) and the fungus can be acquired while petting or grooming an animal. Ringworm can also be acquired from other animals such as horses, pigs, ferrets and cows. The fungus can also be spread by touching inanimate objects like personal care products, bed linen, combs, athletic gear, or hair brushes contaminated by an affected person.

Individuals at high risk of acquiring ringworm include those who:

- Live in crowded, humid conditions.

- Sweat excessively, as sweat can produce a humid wet environment where the pathogenic fungi can thrive. This is most common in the armpits, groin creases and skin folds of the abdomen.

- Participate in close contact sports like soccer, rugby, or wrestling.

- Wear tight, constrictive clothing with poor aeration.

- Have a weakened immune system (e.g., those infected with HIV or taking immunosuppressive drugs).

According to the National Health Service, "Athlete’s foot is very contagious and can be spread through direct and indirect contact." The disease may spread to others directly when they touch the infection. People can contract the disease indirectly by coming into contact with contaminated items (clothes, towels, etc.) or surfaces (such as bathroom, shower, or locker room floors). The fungi that cause athlete's foot can easily spread to one's environment. Fungi rub off of fingers and bare feet, but also travel on the dead skin cells that continually fall off the body. Athlete's foot fungi and infested skin particles and flakes may spread to socks, shoes, clothes, to other people, pets (via petting), bed sheets, bathtubs, showers, sinks, counters, towels, rugs, floors, and carpets.

When the fungus has spread to pets, it can subsequently spread to the hands and fingers of people who pet them. If a pet frequently gnaws upon itself, it might not be fleas it is reacting to, it may be the insatiable itch of tinea.

One way to contract athlete's foot is to get a fungal infection somewhere else on the body first. The fungi causing athlete's foot may spread from other areas of the body to the feet, usually by touching or scratching the affected area, thereby getting the fungus on the fingers, and then touching or scratching the feet. While the fungus remains the same, the name of the condition changes based on where on the body the infection is located. For example, the infection is known as tinea corporis ("ringworm") when the torso or limbs are affected or tinea cruris (jock itch or dhobi itch) when the groin is affected. Clothes (or shoes), body heat, and sweat can keep the skin warm and moist, just the environment the fungus needs to thrive.

Besides being exposed to any of the modes of transmission presented above, there are additional risk factors that increase one's chance of contracting athlete's foot. Persons who have had athlete's foot before are more likely to become infected than those who have not. Adults are more likely to catch athlete's foot than children. Men have a higher chance of getting athlete's foot than women. People with diabetes or weakened immune systems are more susceptible to the disease. HIV/AIDS hampers the immune system and increases the risk of acquiring athlete's foot. Hyperhidrosis (abnormally increased sweating) increases the risk of infection and makes treatment more difficult.

Because fungi prefer warm, moist environments, preventing ringworm involves keeping skin dry and avoiding contact with infectious material. Basic prevention measures include:

- Washing hands after handling animals, soil, and plants.

- Avoiding touching characteristic lesions on other people.

- Wearing loose-fitting clothing.

- Practicing good hygiene when participating in sports that involve physical contact with other people.

Advice often given includes:

- Avoid sharing clothing, sports equipment, towels, or sheets.

- Wash clothes in hot water with fungicidal soap after suspected exposure to ringworm.

- Avoid walking barefoot; instead wear appropriate protective shoes in locker rooms and sandals at the beach.

- Avoid touching pets with bald spots, as they are often carriers of the fungus.

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".

no approved human vaccine exist against "Dermatophytosis". For horses, dogs and cats there is available an approved inactivated vaccine called "Insol Dermatophyton" (Boehringer Ingelheim) which provides time-limited protection against several trichophyton and microsporum fungal strains.

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.

Tinea capitis caused by species of "Microsporum" and "Trichophyton" is a contagious disease that is endemic in many countries. Affecting primarily pre-pubertal children between 6 and 10 years, it is more common in males than females; rarely does the disease persist past age sixteen. Because spread is thought to occur through direct contact with afflicted individuals, large outbreaks have been known to occur in schools and other places where children are in close quarters; however, indirect spread through contamination with infected objects ("fomites") may also be a factor in the spread of infection. In the USA, tinea capitis is thought to occur in 3-8% of the pediatric population; up to one-third of households with contact with an infected person may harbor the disease without showing any symptoms.

The fungal species responsible for causing tinea capitis vary according to the geographical region, and may also change over time. For example, "Microsporum audouinii" was the predominant etiological agent in North America and Europe until the 1950s, but now "Trichophyton tonsurans" is more common in the USA, and becoming more common in Europe and the United Kingdom. This shift is thought to be due to the widespread use of griseofulvin, which is more effective against "M. audounii" than "T. tonsurans"; also, changes in immigration patterns and increases in international travel have likely spread "T. tonsurans" to new areas. Another fungal species that has increased in prevalence is "Trichophyton violaceum", especially in urban populations of the United Kingdom and Europe.

Erythrasma is caused by "Corynebacterium minutissimum". This bacteria tends to thrive in mostly moist and warm environments. Great contributors are poor hygiene, obesity, hyperhidrosis, aging, diabetes mellitus, and a poor immune system. Only some of the causable factors can be looked at for prevention. Hygiene can be improved, along with avoiding moist and warm environments. The other medical factors causing the erythrasma are underlying diseases that cannot be prevented as easily, which at times, can make this condition inevitable.

"Corynebacterium minutissimum" is the bacteria that causes this infection, often club shaped rods when observed under a microscope following a staining procedure, which is a result of snapping division which makes them look like a picket fence. This bacteria is gram positive which means it has a very thick cell wall that cannot be easily penetrated.Electron microscopy confirms the bacterial nature of erythrasma, it shows decreased electron density in keratinized cells at the sites of proliferation. This means that the bacteria causes erythrasma by breaking down keratin Fibrils in the skin. "Corynebacterium minutissimum" consumes carbohydrates such as glucose, dextrose, sucrose, maltose, and mannitol.

Erythrasma manifests mostly in slightly webbed spaces between toes (or other body region skin folds like the thighs/groin area) in warm atmospheric regions, more prevalent in dark skinned humans. As a person ages, they are more susceptible to this infection. This bacterium is not only found in warm atmospheric regions, but also warm and sweaty parts of the human body. "Corynebacterium minutissimum" survives the best here due to the encouraged fungal growth in these regions and allows it to replicate. It is more prevalent in African Americans due to their skin pigmentation.

Guttate psoriasis accounts for approximately 2% of psoriasis cases.

It may appear as thickened, scaly, and sometimes boggy swellings, or as expanding raised red rings (ringworm). Common symptoms are severe itching of the scalp, dandruff, and bald patches where the fungus has rooted itself in the skin. It often presents identically to dandruff or seborrheic dermatitis. The highest incidence in the United States of America is in American boys of school age.

There are three type of tinea capitis, microsporosis, trichophytosis, and favus; these are based on the causative microorganism, and the nature of the symptoms. In "microsporosis", the lesion is a small red papule around a hair shaft that later becomes scaly; eventually the hairs break off 1–3 mm above the scalp. This disease used to be caused primarily by "Microsporum audouinii", but in Europe, "M. canis" is more frequently the causative fungus. The source of this fungus is typically sick cats and kittens; it may be spread through person to person contact, or by sharing contaminated brushes and combs. In the United States, "Trichophytosis" is usually caused by "Trichophyton tonsurans", while "T. violaceum" is more common in Eastern Europe, Africa, and India. This fungus causes dry, non-inflammatory patches that tend to be angular in shape. When the hairs break off at the opening of the follicle, black dots remain. "Favus" is caused by "T. schoenleinii", and is endemic in South Africa and the Middle East. It is characterized by a number of yellowish, circular, cup-shaped crusts (scutula) grouped in patches like a piece of honeycomb, each about the size of a split pea, with a hair projecting in the center. These increase in size and become crusted over, so that the characteristic lesion can only be seen around the edge of the scab.

A dermatomycosis is a skin disease caused by a fungus. This excludes dermatophytosis.

Examples of dermatomycoses are tinea and cutaneous candidiasis.

Genetic and environmental factors can influence the predilection for guttate psoriasis. Human leukocyte antigens, especially those in the HLA-C group are associated with the skin disorder. Beta-hemolytic streptococci infection is the major contributing environmental factor. The typical route of infection is the upper respiratory system. Rarely it is also caused by a skin infection surrounding the anus (perianal streptococcal dermatitis).

With no particular affinity to any particular ethnic group, seen in all age groups and equally amongst males and females, the precise prevalence is not known.

Other rashes that occur in a widespread distribution can look like an id reaction. These include atopic dermatitis, contact dermatitis, dyshidrosis, photodermatitis, scabies and drug eruptions.

Cutaneous larva migrans (abbreviated CLM) is a skin disease in humans, caused by the larvae of various nematode parasites of the hookworm family (Ancylostomatidae). The most common species causing this disease in the Americas is "Ancylostoma braziliense". These parasites live in the intestines of dogs, cats, and wild animals and should not be confused with other members of the hookworm family for which humans are definitive hosts, namely "Ancylostoma duodenale" and "Necator americanus".

Colloquially called creeping eruption due to its presentation, the disease is also somewhat ambiguously known as "ground itch" or (in some parts of the Southern USA) "sandworms", as the larvae like to live in sandy soil. Another vernacular name is plumber's itch. The medical term CLM literally means "wandering larvae in the skin".

Other causes include poor immune system function such as from HIV/AIDS, diabetes, malnutrition, or alcoholism. Poor hygiene and obesity have also been linked. It may occur following antibiotic use due to the development of resistance to the antibiotics used. An associated skin disease favors recurrence. This may be attributed to the persistent colonization of abnormal skin with "S. aureus" strains, such as is the case in persons with atopic dermatitis.

Boils which recur under the arm, breast or in the groin area may be associated with hidradenitis suppurativa (HS).

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.

CLM can be treated in a number of different ways:

- Systemic (oral) agents include albendazole (trade name "Albenza") and ivermectin (trade name "Stromectol")).

- Another agent which can be applied either topically "or" taken by mouth is thiabendazole (trade name "Mintezol")), an anti-helminthic.

- Topical freezing agents, such as ethylene chloride or liquid nitrogen, applied locally can freeze and kill the larvae, but this method has a high failure rate because the larvae are usually located away from the site of the visible skin trails. Additionally, this is a painful method which can cause blistering and/or ulceration of the skin and it is therefore not recommended.

- It is recommended to use Benadryl or some anti-itch cream (i.e. Cortizone or Calamine lotion). This will help relieve some of the itch.

- Wearing shoes in areas where these parasites are known to be endemic offers protection from infection. In general, avoiding exposure of skin to contaminated soil or sand offers the best protection. In some areas dogs have been banned from beaches in an attempt to control human infection.

A 1992 study of 163 affected persons found that most patients had no other medical problems and most manage to lead a relatively normal life.

Vulvitis, inflammation of the vulva, can have a variety of etiologies in children and adolescents, including allergic dermatitis, contact dermatitis, lichen sclerosus, and infections with bacteria, fungi, and parasites. Dermatitis in infants is commonly caused by a soiled diaper being left on for an extended period of time. Increasing the frequency of diaper changes and topical application of emollients are sufficient to resolve most cases. Dermatitis of the vulva in older children is usually caused by exposure to an irritant (e.g. scented products that come into contact with the vulva, laundry detergent, soaps, etc.) and is treated with preventing exposure and encouraging sitz baths with baking soda as the vulvar skin heals. Other treatment options for vulvar dermatitis include oral hydroxyzine hydrochloride or topical hydrocortisone.

Lichen sclerosus is another common cause of vulvitis in children, and it often affects an hourglass or figure eight-shaped area of skin around the anus and vulva. Symptoms of a mild case include skin fissures, loss of skin pigment (hypopigmentation), skin atrophy, a parchment-like texture to the skin, dysuria, itching, discomfort, and excoriation. In more severe cases, the vulva may become discolored, developing dark purple bruising (ecchymosis), bleeding, scarring, attenuation of the labia minora, and fissures and bleeding affecting the posterior fourchette. Its cause is unknown, but likely genetic or autoimmune, and it is unconnected to malignancy in children. If the skin changes are not obvious on visual inspection, a biopsy of the skin may be performed to acquire an exact diagnosis. Treatment for vulvar lichen sclerosus may consist of topical hydrocortisone in mild cases, or stronger topical steroids (e.g. clobetasol propionate). Preliminary studies show that 75% of cases do not resolve with puberty.

Organisms responsible for vulvitis in children include pinworms ("Enterobius vermicularis"), "Candida" yeast, and group A hemolytic "Streptococcus". Though pinworms mainly affect the perianal area, they can cause itching and irritation to the vulva as well. Pinworms are treated with albendazole. Vulvar "Candida" infections are uncommon in children, and generally occur in infants after antibiotic therapy, and in children with diabetes or immunodeficiency. "Candida" infections cause a red raised vulvar rash with satellite lesions and clear borders, and are diagnosed by microscopically examining a sample treated with potassium hydroxide for hyphae. They are treated with topical butoconazole, clotrimazole, or miconazole. "Streptococcus" infections are characterized by a dark red discoloration of the vulva and introitus, and cause pain, itching, bleeding, and dysuria. They are treated with antibiotics.

Darier's disease (DAR), also known as Darier disease, Darier–White disease, Dyskeratosis follicularis and Keratosis follicularis, is an autosomal dominant disorder discovered by French dermatologist Ferdinand-Jean Darier. Darier's is characterized by dark crusty patches on the skin, sometimes containing pus. The crusty patches are also known as keratotic papules, keratosis follicularis or dyskeratosis follicularis.

Mild forms of the disease are the most common, consisting solely of skin rashes that flare up under certain conditions such as high humidity, high stress or tight-fitting clothes. Even in mild forms, short stature combined with poorly formed fingernails containing vertical striations are diagnostic.

"Candida" yeasts are generally present in healthy humans, frequently part of the human body's normal oral and intestinal flora, and particularly on the skin; however, their growth is normally limited by the human immune system and by competition of other microorganisms, such as bacteria occupying the same locations in the human body.

"Candida" requires moisture for growth, notably on the skin. For example, wearing wet swimwear for long periods of time is believed to be a risk factor. In extreme cases, superficial infections of the skin or mucous membranes may enter into the bloodstream and cause systemic "Candida" infections.

Factors that increase the risk of candidiasis include HIV/AIDS, mononucleosis, cancer treatments, steroids, stress, antibiotic usage, diabetes, and nutrient deficiency. Hormone replacement therapy and infertility treatments may also be predisposing factors. Treatment with antibiotics can lead to eliminating the yeast's natural competitors for resources in the oral and intestinal flora; thereby increasing the severity of the condition. A weakened or undeveloped immune system or metabolic illnesses are significant predisposing factors of candidiasis. Almost 15% of people with weakened immune systems develop a systemic illness caused by "Candida" species. Diets high in simple carbohydrates have been found to affect rates of oral candidiases.

"C. albicans" was isolated from the vaginas of 19% of apparently healthy women, i.e., those who experienced few or no symptoms of infection. External use of detergents or douches or internal disturbances (hormonal or physiological) can perturb the normal vaginal flora, consisting of lactic acid bacteria, such as lactobacilli, and result in an overgrowth of "Candida" cells, causing symptoms of infection, such as local inflammation. Pregnancy and the use of oral contraceptives have been reported as risk factors. Diabetes mellitus and the use of antibiotics are also linked to increased rates of yeast infections.

In penile candidiasis, the causes include sexual intercourse with an infected individual, low immunity, antibiotics, and diabetes. Male genital yeast infections are less common, but a yeast infection on the penis caused from direct contact via sexual intercourse with an infected partner is not uncommon.