Nummular dermatitis is characterized by chronic or relapsing itchy coin-sized ovoid-shaped red plaques. They can occur on the trunk, limbs, face, and hands.

Erythroderma is generalized exfoliative dermatitis, which involves 90% or more of the patient's skin. The most common cause of erythroderma is exacerbation of an underlying skin disease, such as psoriasis, contact dermatitis, seborrheic dermatitis, lichen planus, pityriasis rubra pilaris or a drug reaction. Primary erythroderma is less frequent and is usually seen in cases of cutaneous T-cell lymphoma, in particular in Sézary's disease.

The most common causes of exfoliative dermatitis are best remembered by the mnemonic device ID-SCALP. The causes and their frequencies are as follows:

- Idiopathic - 30%

- Drug allergy - 28%

- Lymphoma and leukemia - 14%

- Atopic dermatitis - 10%

- Psoriasis - 8%

- Contact dermatitis - 3%

- Seborrheic dermatitis - 2%

Differential diagnosis in patients with erythroderma may be difficult.

Diagnosis of nummular dermatitis largely clinical. Biopsies are typically not necessary, and cannot be used to rule out other atopic dermatitis or other eczemas. However, patch testing may be employed to rule out irritants (contact dermatitis) as a cause. In children, nummular dermatitis is commonly confused with tinea corporis.

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.

A stinging and burning sensation with rash is often felt and noticed, but itching is less common. Often the rash is steroid responsive, initially improving with application of topical steroid. The redness caused by perioral dermatitis has been associated with variable level of depression.

Initially, there may be small pinpoint papule either side of the nostrils. Multiple small (1-2mm) papules and pustules then occur around the mouth, nose and sometimes cheeks. The area of skin directly adjacent to the lips, also called the vermillion border, is spared and looks normal. There may be some mild background redness and occasional scale. These areas of skin are felt to be drier and therefore there is a tendency to moisturise them more frequently. Hence, they do not tolerate drying agents well and the rash can be worsened by them.

Perioral dermatitis is also known by other names including rosacea-like dermatoses, periorofacial dermatitis and periorificial dermatitis.

Unlike rosacea which involves mainly the nose and cheeks, there is no telangiectasia in perioral dermatitis. Rosacea also has a tendency to be present in older people. Acne can be distinguished by the presence of comedones and by its wider distribution on the face and chest. There are no comedones in personal dermatitis.

Other skin diseases which may resemble perioral dermatitis include:

- Rosacea

- Acne vulgaris

- Seborrheic dermatitis

- Allergic contact dermatitis

- Irritant contact dermatitis

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

Erythroderma (also known as "Exfoliative dermatitis," "Dermatitis exfoliativa") is an inflammatory skin disease with erythema and scaling that affects nearly the entire cutaneous surface.

In ICD-10, a distinction is made between "exfoliative dermatitis" at L26, and "erythroderma" at L53.9.

The diagnosis of IDD is made clinically, by observing the limitation of an erythematous eruption to the convex surfaces of the genital area and buttocks. If the diaper dermatitis occurs for greater than 3 days it may be colonized with "Candida albicans", giving it the beefy red, sharply marginated, appearance of diaper candidiasis.

Other rashes that occur in the diaper area include seborrhoeic dermatitis and atopic dermatitis. Both Seborrheic and Atopic dermatitis require individualized treatment; they are not the subject of this article.

- Seborrheic dermatitis, typified by oily, thick yellowish scales, is most commonly seen on the scalp (cradle cap) but can also appear in the inguinal folds.

- Atopic dermatitis, or eczema, is associated with allergic reaction, often hereditary. This class of rashes may appear anywhere on the body and is characterized by intense itchiness.

Perioral dermatitis is a type of skin rash. Symptoms include multiple small (1–2 mm) bumps and blisters with sometimes background redness and scale, localized to the skin around the mouth and nostrils. Less commonly the eyes and genitalia may be involved. It can be persistent or recurring and resembles particularly rosacea and to some extent acne and allergic dermatitis. The term dermatitis is a misnomer because this is not an eczematous process.

The cause is unclear. Topical steroids are associated with the condition and moisturizers and cosmetics may contribute. The underlying mechanism may involve blockage of the skin surface followed by subsequent excessive growth of skin flora. Fluorinated toothpaste and some micro-organisms including candida may also worsen the condition, but their roles in this condition is unclear. It is considered a disease of the hair follicle with biopsy samples showing microscopic changes around the hair follicle. Diagnosis is based on symptoms.

Treatment is typically by stopping topical steroids, changing cosmetics, and in more severe cases, taking tetracyclines by mouth. Stopping steroids may initially worse the rash. The condition is estimated to affect 0.5-1% of people a year in the developed world. Up to 90% of those affected are women between the ages of 16 and 45 years, though it also affects children and the elderly, and has an increasing incidence in men.

Discoid eczema (nummular eczema, exudative eczema, microbial eczema) is characterized by round spots of oozing or dry rash, with clear boundaries, often on lower legs. It is usually worse in winter. Cause is unknown, and the condition tends to come and go. (ICD-10 L30.0)

Venous eczema (gravitational eczema, stasis dermatitis, varicose eczema) occurs in people with impaired circulation, varicose veins, and edema, and is particularly common in the ankle area of people over 50. There is redness, scaling, darkening of the skin, and itching. The disorder predisposes to leg ulcers. (ICD-10 I83.1)

Dermatitis gangrenosa (also known as "Gangrene of the skin") is a cutaneous condition caused by infection by Clostridium resulting in a necrosis and sloughing of the skin.

Id reactions (also known as "disseminated eczema," and "generalized eczema") are types of acute dermatitis developing after days or weeks at skin locations distant from the initial inflammatory or infectious site. They can be localised or generalised. This is also known as an 'autoeczematous response' and there must be an identifiable initial inflammatory or infectious skin problem which leads to the generalised eczema. Often, intensely itchy, the red papules and pustules can also be associated with blisters and scales and are always remote from the primary lesion. It is most commonly a blistering rash with itchy vesicles on the sides of fingers and feet as a reaction to fungal infection on the feet, athlete's foot. Stasis dermatitis, Allergic contact dermatitis, Acute irritant contact eczema and Infective dermatitis have been documented as possible triggers, but the exact cause and mechanism is not fully understood. Several other types of id reactions exist including erythema nodosum, erythema multiforme, Sweet's syndrome and urticaria.

Although there are a multitude of varying appearances, the id reaction often presents with symmetrical red patches of eczema with papules and vesicles, particularly on the outer sides of the arms, face and trunk which occur suddenly and are intensely itchy occur a few days to a week after the initial allergic or irritant dermatitis. Most commonly, athletes foot can lead to localised vesicles on hands, bacterial infections to erythema nodosum and herpes simplex virus to erythema multiforme.

The diagnosis is frequently made by treating the initial triggering skin problem and observing the improvement in the eczematous rash. Both the initial skin problem and the id reaction must be observed to make the diagnosis.

All dyshidrotic rashes are not id reactions, but id reactions are often dishydrotic-like.

Initial tests may include isolating a fungus by taking a swab and sending it for culture. Patch testing may be considered if there is suspicion of allergic contact dermatitis.

A skin biopsy is rarely necessary, but if done mostly shows an interstitial granulomatous dermatitis, some lesions being spongiotic. Id reactions cannot be distinguished from other skin diseases by histopathology. However, they can be distinguished from other id reactions by histopathology.

Redness around the lips in circumoral distribution with dryness and scale is typical. Chapping may also occur, especially in cold weather.

People with AD often have dry and scaly skin that spans the entire body, except perhaps the diaper area, and intensely itchy red, splotchy, raised lesions to form in the bends of the arms or legs, face, and neck.

AD commonly occurs on the eyelids where signs such as Dennie-Morgan infraorbital fold, infra-auricular fissure, periorbital pigmentation can be seen. Post-inflammatory hyperpigmentation on the neck gives the classic 'dirty neck' appearance. Lichenification, excoriation and erosion or crusting on the trunk may indicate secondary infection. Flexural distribution with ill-defined edges with or without hyperlinearily on the wrist, finger knuckles, ankle, feet and hand are also commonly seen.

The intense contact between a musical instrument and skin may exaggerate existing skin conditions or cause new skin skin conditions. Skin conditions like hyperhidrosis, lichen planus, psoriasis, eczema, and urticaria may be caused in instrumental musicians due to occupational exposure and stress. Allergic contact dermatitis and irritant contact dermatitis are the most common skin conditions seen in string musicians.

CGPD is characterized by the presence of small, raise, dome-shape papules primarily distributed around the mouth, eyes, and nose. Affected children may also have papules on the ears, eyelids, cheeks, forehead, and nose. CGPD skin lesions affecting areas of the skin other than the face are rare.

Acneiform eruptions are a group of dermatoses including acne vulgaris, rosacea, folliculitis, and perioral dermatitis. Restated, acneiform eruptions are follicular eruptions characterized by papules and pustules resembling acne.

The hybrid term "acneiform", literally, refers to an appearance similar to acne.

The terminology used in this field can be complex, and occasionally contradictory. Some sources consider acne vulgaris part of the differential diagnosis for an acneiform eruption. Other sources classified acne vulgaris under acneiform eruption. MeSH explicitly excludes perioral dermatitis from the category of "acneiform eruptions", though it does group acneiform eruptions and perioral dermatitis together under "facial dermatoses".

Once pederin is on the skin from the initial beetle contact, it may also be spread elsewhere on the skin. "Kissing" or "mirror-image" lesions where two skin areas come in contact (for example, the elbow flexure) are often seen. Washing the hands and skin with soap and water is strongly recommended, if contact with a rove beetle has occurred.

Initial skin contact with pederin shows no immediate result. Within 12–36 hours, however, a reddish rash (erythema) appears, which develops into blisters. Irritation, including crusting and scaling, may last from two to three weeks.

One study reported best results with a treatment regimen that combined topical steroids with oral antihistamines and antibiotics. The authors hypothesized that antibiotics were helpful because of the possible contamination of skin by pederin-producing bacteria.

Dermatitis herpetiformis is characterized by intensely itchy, chronic papulovesicular eruptions, usually distributed symmetrically on extensor surfaces (buttocks, back of neck, scalp, elbows, knees, back, hairline, groin, or face). The blisters vary in size from very small up to 1 cm across.

The condition is extremely itchy, and the desire to scratch can be overwhelming. This sometimes causes the sufferer to scratch the blisters off before they are examined by a physician. Intense itching or burning sensations are sometimes felt before the blisters appear in a particular area.

Untreated, the severity of DH can vary significantly over time, in response to the amount of gluten ingested.

Dermatitis herpetiformis symptoms typically first appear in the early years of adulthood between 20 and 30 years of age.

Although the first signs and symptoms of dermatitis herpetiformis are intense itching and burning, the first visible signs are the small papules or vesicles that usually look like red bumps or blisters. The rash rarely occurs on other mucous membranes, excepting the mouth or lips. The symptoms range in severity from mild to serious, but they are likely to disappear if gluten ingestion is avoided and appropriate treatment is administered.

Dermatitis herpetiformis symptoms are chronic, and they tend to come and go, mostly in short periods of time. Sometimes, these symptoms may be accompanied by symptoms of coeliac disease, commonly including abdominal pain, bloating or loose stool, and fatigue.

The rash caused by dermatitis herpetiformis forms and disappears in three stages. In the first stage, the patient may notice a slight discoloration of the skin at the site where the lesions appear. In the next stage, the skin lesions transform into obvious vesicles and papules that are likely to occur in groups. Healing of the lesions is the last stage of the development of the symptoms, usually characterized by a change in the skin color. This can result in areas of the skin turning darker or lighter than the color of the skin on the rest of the body. Because of the intense itching, patients usually scratch, which can lead to the formation of crusts.

Seborrhoeic dermatitis' symptoms appear gradually, and usually the first signs are flaky skin and scalp. Symptoms occur most commonly anywhere on the skin of the scalp, behind the ears, on the face, and in areas where the skin folds. Flakes may be yellow, white or grayish. Redness and flaking may also occur on the skin near the eyelashes, on the forehead, around the sides of the nose, on the chest, and on the upper back.

In more severe cases, yellowish to reddish scaly pimples appear along the hairline, behind the ears, in the ear canal, on the eyebrows, on the bridge of the nose, around the nose, on the chest, and on the upper back.

Commonly, patients experience mild redness, scaly skin lesions and in some cases hair loss. Other symptoms include patchy scaling or thick crusts on the scalp, red, greasy skin covered with flaky white or yellow scales, itching, soreness and yellow or white scales that may attach to the hair shaft.

Seborrhoeic dermatitis can occur in infants younger than three months and it causes a thick, oily, yellowish crust around the hairline and on the scalp. Itching is not common among infants. Frequently, a stubborn diaper rash accompanies the scalp rash. Usually, when it occurs in infants the condition resolves itself within days and with no treatment.

In adults, symptoms of seborrhoeic dermatitis may last from a few weeks, to years. Many patients experience alternating periods of inflammation. The condition is referred to a specialist when self-care has proven unsuccessful.

The signs and symptoms of dandruff are an itchy scalp and flakiness. Red and greasy patches of skin and a tingly feeling on the skin are also symptoms.

Autosensitization dermatitis (or cutaneous autosensitization) presents with the development of widespread dermatitis or dermatitis distant from a local inflammatory focus, a process referred to as autoeczematization.