Lesions of erythrasma are initially pink, but progress quickly to become brown and scaly (as skin starts to shed), which are sharply distinguished. Erythrasmic patches are typically found in moist and intertriginous areas (skin fold areas—e.g. armpit, groin, under breast) and can be well-defined patches or irregular. The most common is interdigital erythrasama, which is of the foot, and may present as a scaling, fissuring, and chronic non-resolving break down of the toe web interspaces.The slightly webbed spaces between toes, or other body region skin folds, make it difficult to distinguish from various Tinea. The patient is commonly otherwise asymptomatic.

Erythrasma is a superficial skin infection that causes brown, scaly skin patches. It is caused by "Corynebacterium minutissimum," a normal part of skin flora (the microorganisms that are normally present on the skin).

There are two types of erythrasma: generalized and interdigital. Interdigital is the most common bacterial infection of the feet and normally does not show any symptoms. Not only is this an aesthetically unappealing condition, but there is evidence to support that disciform erythrasma can be an early sign of type 2 diabetes mellitus. The generalized erythrasma is most commonly seen in Diabetes mellitus type 2 where the lesions go beyond the areas of the body where skin is rubbing together. It is prevalent among diabetics and the obese, and in warm climates; it is worsened by wearing occlusive clothing.

The presence of erythrasma is approximately 4% and is more likely to be found in the subtropical and tropical areas compared to the rest of the world. It is found more commonly in African Americans due to the darker skin and even though both sexes are affected, it is usually found more frequently in males for the thigh and leg regions. A great contributor to this infection is a weakened immune system which comes with aging, therefore the elderly are more susceptible to this disease than the young; this does not mean the young cannot be affected. The epidemiology background of erythrasma remains partially unsolved.

"Trench foot " is a medical condition caused by prolonged exposure of the feet to damp, unsanitary, and cold conditions. The use of the word "trench" in the name of this condition is a reference to trench warfare, mainly associated with World War I. Affected feet may become numb, affected by erythrosis (turning red) or cyanosis (turning blue) as a result of poor vascular supply, and feet may begin to have a decaying odour due to the possibility of the early stages of necrosis setting in. As the condition worsens, feet may also begin to swell. Advanced trench foot often involves blisters and open sores, which lead to fungal infections; this is sometimes called tropical ulcer (jungle rot).

If left untreated, trench foot usually results in gangrene, which can cause the need for amputation. If trench foot is treated properly, complete recovery is normal, though it is marked by severe short-term pain when feeling returns. As with other cold-related injuries, trench foot leaves sufferers more susceptible to it in the future.

"Tropical immersion foot" (also known as "Paddy foot", and "Paddy-field foot") is a skin condition of the feet seen after continuous immersion of the feet in water or mud of temperature above 22 degrees Celsius (roughly 72 degrees Fahrenheit ) for two to ten days.

The skin typically presents as red and hot. These infections can be painful.

Pus is usually present, along with gradual thickening and browning discoloration of the nail plate.

Intense rubbing can cause a blister, as can any friction on the skin if continued long enough. This kind of blister is most common after walking long distances or by wearing old or poorly fitting shoes. Blisters are most common on the hands and feet, as these extremities are susceptible while walking, running, or performing repetitive motions, such as joystick manipulation whilst playing certain video games, digging with a shovel, playing guitar, etc. Blisters form more easily on moist skin than on dry or soaked skin, and are more common in warm conditions. Less-aggressive rubbing over long periods of time may cause calluses to form rather than a blister. Both blisters and calluses can lead to more serious complications, such as foot ulceration and infection, particularly when sensation or circulation is impaired, as in the case of diabetes, neuropathy or peripheral artery disease (PAD).

A blister may form when the skin has been damaged by friction or rubbing, heat, cold or chemical exposure. Fluid collects between the epidermisthe upper layer of the skinand the layers below. This fluid cushions the tissue underneath, protecting it from further damage and allowing it to heal.

Moist desquamation is a description of the clinical pattern seen as a consequence of radiation exposure where the skin thins and then begins to weep because of loss of integrity of the epithelial barrier and decreased oncotic pressure. Typically this occurs at doses of 15–20 Gray, far higher than any diagnostic scan and more typical of levels seen in radiotherapy or deployment of nuclear armament. Historically, this was a common phenomenon in Hiroshima and Nagasaki during World War II with the atomic bomb attacks from the United States.

The phenomenon was famously described by John Hersey in his article, and later book, Hiroshima.

It may have a variety of appearances; most easily identifiable are the enlarging raised red rings with a central area of clearing (ringworm). The same appearances of ringworm may also occur on the scalp (tinea capitis), beard area (tinea barbae) or the groin (tinea cruris, known as jock itch or dhobi itch).

Other classic features of tinea corporis include:

- The edge of the rash appears elevated and is scaly to touch.

- Sometimes the skin surrounding the rash may be dry and flaky.

- Almost invariably, there will be hair loss in areas of the infection.

The hard part at the center of the corn resembles a barley seed, that is like a funnel with a broad raised top and a pointed bottom. Because of their shape, corns intensify the pressure at the tip and can cause deep tissue damage and ulceration. Hard corns are especially problematic for people with insensitive skin due to damaged nerves (e.g., in people with diabetes mellitus). The scientific name for a corn is "heloma" (plural "helomata"). A hard corn is called a "heloma durum", while a soft corn is called a "heloma molle".

The location of soft corns tends to differ from that of hard corns. Hard corns occur on dry, flat surfaces of skin. Soft corns (frequently found between adjacent toes) stay moist, keeping the surrounding skin soft. The corn's center is not soft, however, but indurated.

A corn (or clavus, plural clavi or clavuses) is a distinctively shaped callus of dead skin that usually occurs on thin or glabrous (hairless and smooth) skin surfaces, especially on the dorsal surface of toes or fingers. They can sometimes occur on the thicker skin of the palms or bottom of the feet.

Corns form when the pressure point against the skin traces an elliptical or semi-elliptical path during the rubbing motion, the center of which is at the point of pressure, gradually widening. If there is constant stimulation of the tissue producing the corns, even after the corn is surgically removed, the skin may continue to grow as a corn.

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.

There are two different manifestations of rainscald: the winter form, which is more severe due to the longer coat of the horse, and the summer form, which is less severe. Horses are usually affected on the back, head, and neck, where insects commonly bite, and the legs, which are commonly infected if the horse is kept in moist footing. Initially, the horse will display a matted coat and bumps which will then progress to crusty scabs and lesions. The animal may also be itchy and display signs of discomfort.

Sloughing of the epidermis and exposure of the dermal layer clinically characterize moist desquamation. Outside of medical therapy, when moist desquamation is seen in the setting of nuclear warfare, the condition is generally thought to be fatal.

Tinea corporis (also known as ringworm, tinea circinata, and tinea glabrosa) is a superficial fungal infection (dermatophytosis) of the arms and legs, especially on glabrous skin; however, it may occur on any part of the body. It is similar to other forms of tinea.

The disease presents with the widespread formation of fluid-filled blisters that are thin walled and easily ruptured and the patient can be positive for Nikolsky's sign. Ritter's Disease of the Newborn is the most severe form of SSSS with similar signs and symptoms. SSSS often includes a widespread painful erythroderma, often involving the face, diaper, and other intertriginous areas. Extensive areas of desquamation might be present. Perioral crusting and fissuring are seen early in the course. Unlike toxic epidermal necrolysis, SSSS spares the mucous membranes. It is most common in children under 6 years, but can be seen in adults who are immunosuppressed or have renal failure.

Intertrigo refers to a type of inflammatory rash (dermatitis) of the superficial skin that occurs within a person's body folds. These areas are more susceptible to irritation and subsequent infection due to factors that promote skin breakdown such as moisture, friction, and exposure to bodily secretions such as sweat, urine or feces. Areas of the body which are more likely to be affected by intertrigo include the inframammary fold, intergluteal cleft, armpits, and spaces between the fingers or toes. Skin affected by intertrigo is more prone to infection than intact skin.

The term "intertrigo" commonly refers to a secondary infection with bacteria (such as "Corynebacterium minutissimum"), fungi (such as "Candida albicans"), or viruses. A frequent manifestation is candidal intertrigo.

Intertrigo occurs more often in warm and humid conditions. Generally, intertrigo is more common in people with a weakened immune system including children, the elderly, and immunocompromised people. The condition is also more common in people who experience urinary incontinence and decreased ability to move.

Hairy tongue largely occurs in the central part of the dorsal tongue, just anterior (in front) of the circumvallate papillae, although sometimes the entire dorsal surface may be involved. Discoloration usually accompanies hairy tongue, and may be yellow, brown or black. Apart from the appearance, the condition is typically asymptomatic, but sometimes people may experience a gagging sensation or a bad taste. There may also be associated oral malodor (intra-oral halitosis).

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

Rainscald (also known as "dermatophilosis", "rain rot" and "streptothricosis") is a common skin disease in horses that is caused by the bacterium "Dermatophilus congolensis". This is the same organism that causes Mud fever in horses. This disease is very common in cows, sheep and goats and is also found occasionally in cats, dogs, and humans. D. congolensis is a gram-positive bacterium that is thought to originate from the soil. It commonly causes disease in moist tropical areas, but can also be found in wet northern environments. Moisture and high temperatures facilitate the dispersal and penetration of zoospores into the skin, contributing to the spread of the disease.

Ticks, biting flies, and contact with other infected animals also causes the spread of rainscald. Once in the skin, the bacteria cause inflammation of the skin as well as the typical symptoms associated with rainscald.

The term hyperkeratosis is often used in connection with lesions of the mucous membranes, such as leukoplakia. Because of the differences between mucous membranes and the skin (e.g. keratinizing mucosa does not have a stratum lucidum and non keratinizing mucosa does not have this layer or normally a stratum corneum or a stratum granulosum), sometimes specialized texts give slightly different definitions of hyperkeratosis in the context of mucosae. Examples are "an excessive formation of keratin (e.g., as seen in leukoplakia)" and "an increase in the thickness of the keratin layer of the epithelium, or the presence of such a layer in a site where none would normally be expected."

Ulcerative dermatitis is a skin disorder in rodents associated with bacterial growth often initiated by self-trauma due to a possible allergic response. Although other organisms can be involved, bacteria culture frequently shows Staphylococcus aureus. Primarily found on the rib cage, neck, and shoulder, lesions are often irregular, circumscribed, and moist. Intense itching may lead to scratching which may aggravate and perpetuate the lesion. Destruction of the epidermis along with underlying pustules or abscesses, and granulomatous inflammation, may be present.

In cases where topical treatment alone does not resolve the dermatitis and irritants are not known, a secondary bacterial, fungal or yeast infection might be present and may require an anti-fungal or antibiotics to be prescribed by the veterinarian to affect a cure.

In rats, this skin disorder may be observed on the neck and head, often secondary to skin trauma from scratches or fighting.

Black hairy tongue (BHT, also termed lingua villosa nigra) refers to a condition of the tongue where the filiform papillae elongate with black or brown discoloration, giving a black and hairy appearance. The appearance may be alarming, but it is a harmless condition. Predisposing factors include smoking, xerostomia (dry mouth), soft diet, poor oral hygiene and certain medications. Management is by improving oral hygiene, especially scraping or brushing the tongue.

Skin plaques start to appear as reddened areas of inflammation, thus often leading to the mistaken diagnosis of Atopic Dermatitis. Following inflammation, the red areas start keratinization, eventually forming the definitive plaques that appear brownish, dry and scaled. Following quite a precise temporal pattern of evolution, the keratinized plaques last for weeks or months, eventually leading to periods of desquamation that leads to the uncovering of "normal" skin. Then, a new cycle usually begins, leaving a variable number of days of delay between the cycles.

Though environmental causes are not well understood, it seems clear that factors like sun exposure, wind and air conditioning add to the degree of skin inflammation that sets the start of a new cycle.

Hyperkeratosis is thickening of the stratum corneum (the outermost layer of the epidermis), often associated with the presence of an abnormal quantity of keratin, and also usually accompanied by an increase in the granular layer. As the corneum layer normally varies greatly in thickness in different sites, some experience is needed to assess minor degrees of hyperkeratosis.

It can be caused by vitamin A deficiency or chronic exposure to arsenic.

Hyperkeratosis can also be caused by B-Raf inhibitor drugs such as Vemurafenib and Dabrafenib.

It can be treated with urea-containing creams, which dissolve the intercellular matrix of the cells of the stratum corneum, promoting desquamation of scaly skin, eventually resulting in softening of hyperkeratotic areas.