Pemphigus is a group of autoimmune blistering diseases that may be classified into the following types:

Pemphigus defines a group of autoimmune interepithelial blistering diseases that are characterized by loss of normal cell-cell adhesion (acantholysis), and by the presence of pathogenic (predominantly IgG) autoantibodies reacting against epithelial adhesion molecules. Pemphigus is further divided in two major subtypes: pemphigus vulgaris (PV) and pemphigus foliaceus (PF). However, several other disorders such as IgA pemphigus, IgE pemphigus, pemphigus herpetiformis, drug induced pemphigus, Senear Usher syndrome and endemic pemphigus foliaceus exist;recognized by a dermatologist from the appearance and distribution of the skin lesions. It is also commonly diagnosed by specialists practicing otolaryngology- head and neck surgery, periodontists, oral and maxillofacial surgeons and eye doctors, as lesions can affect the eyes and mucous membrane of the oral cavity. Intraorally it resembles the more common diseases lichen planus and mucous membrane pemphigoid. Definitive diagnosis requires examination of a skin or mucous membrane biopsy by a dermatopathologist or oral pathologist. The skin biopsy is taken from the edge of a blister, prepared for histopathology and examined with a microscope. The pathologist looks for an intraepidermal vesicle caused by the breaking apart of epidermal cells (acantholysis). Thus, the superficial (upper) portion of the epidermis sloughs off, leaving the bottom layer of cells on the "floor" of the blister. This bottom layer of cells is said to have a "tombstone appearance".

Definitive diagnosis also requires the demonstration of anti-desmoglein autoantibodies by direct immunofluorescence on the skin biopsy. These antibodies appear as IgG deposits along the desmosomes between epidermal cells, a pattern reminiscent of chicken wire. Anti-desmoglein antibodies can also be detected in a blood sample using the ELISA technique.

Because it is a rare disease, diagnosis is often complicated and takes a long time. Early in the disease patients may have erosions in the mouth or blisters on the skin. These blisters can be itchy or painful. Theoretically, the blisters should demonstrate a positive Nikolsky's sign, in which the skin sloughs off from slight rubbing, but this is not always reliable. The gold standard for diagnosis is a punch biopsy from the area around the lesion that is examined by direct immunofluorescent staining, in which cells are acantholytic, that is, lacking the normal intercellular connections that hold them together. These can also be seen on a Tzanck smear. These cells are basically rounded, nucleated keratinocytes formed due to antibody mediated damage to cell adhesion protein desmoglein.

Pemphigus vulgaris is easily confused with impetigo and candidiasis. IgG4 is considered pathogenic. The diagnosis can be confirmed by testing for the infections that cause these other conditions, and by a lack of response to antibiotic treatment.

Diagnosis is based on two biopsies of the skin, one submitted for routine H&E staining and one for immunofluorescence studies.

Lichen planus has a unique microscopic appearance that is similar between cutaneous, mucosal and oral. A Periodic acid-Schiff stain of the biopsy may be used to visualise the specimen. Histological features seen include:

- thickening of the stratum corneum both with nuclei present (parakeratosis) and without (orthokeratosis). Parakeratosis is more common in oral variants of lichen planus.

- thickening of the stratum granulosum

- thickening of the stratum spinosum (acanthosis) with formation of colloid bodies (also known as Civatte bodies, Sabouraud bodies) that may stretch down to the lamina propria.

- liquefactive degeneration of the stratum basale, with separation from the underlying lamina propria, as a result of desmosome loss, creating small spaces (Max Joseph spaces).

- Infiltration of T cells in a band-like pattern into the dermis "hugging" the basal layer.

- Development of a "saw-tooth" appearance of the rete pegs, which is much more common in non-oral forms of lichen planus.

The differential diagnosis for OLP includes:

- Other oral vesiculo-ulcerative conditions such as Pemphigus vulgaris and Benign mucous membrane pemphigoid

- Lupus erythematosus, with lesions more commonly occur on the palate and appear as centrally ulcerated or erythematous with radiating white striae. In contrast, OLP and lichenoid reactions rarely occur on the palate, and the striae are randomly arranged rather than radial.

- Chronic ulcerative stomatitis

- Frictional keratosis and Morsicatio buccarum (chronic cheek biting)

- Oral leukoplakia

- Oral candidiasis

Diagnostic techniques:

- antibodies (IgG) precipitates complement (C3) in the lamina lucida of the basement membrane.

- Circulating auto-antibodies to BP-1 antigen (located in hemidesmosome). 50% have BP-2.

- Positive Nikolsky sign.

- IgG, C3 deposition at BM creating smooth line in immunofluorescent analysis.

Research into using genetically modified T-cells to treat pemphigus vulgaris in mice was reported in 2016. Rituximab indiscriminately attacks all B cells, which reduces the body's ability to control infections. In the experimental treatment, human T cells are genetically engineered to recognize only those B cells that produce antibodies to desmoglein 3.

Bullous pemphigoid may be self-resolving in a period ranging from several months to many years even without treatment. Poor general health related to old age is associated with a poorer prognosis.

Patients with high concentration of antibodies show intercellular, intraepidermal antibodies as well as along the dermoepidermal junction. Patients with low concentration of antibodies only present with them inside the cells (intercellular).

If the results are negative, perform the additional assays regardless. Cases have been confirmed that reported with initial negative DIF and IDIF tests.

Immunoprecipitation, immunoblotting and enzyme-link immunosorbent assay (ELISA)

Poot et al. 2013 determined that immunoprecipitation for antibodies against envoplakin and periplakin or alpha2-macroglobulin-like–1 is the most sensitive test. However, alpha2-macroglobulin-like-1 can also be detected in patients with toxic epidermal necrosis.

Pemphigoid is usually considered to be mediated by IgG, but IgA-mediated forms have also been described.

IgA-mediated immunobullous diseases can often be difficult to treat even with usually effective medications such as rituximab.

While the term pemphigus typically refers to "a rare group of blistering autoimmune diseases" affecting "the skin and mucous membranes", Hailey–Hailey disease is not an autoimmune disorder and there are no autoantibodies. According to Pemphigus Pemphigoid Foundation (IPPF), "familial benign chronic pemphigus, or Hailey-Hailey disease, is a different condition from Pemphigus".

The management depends upon the severity of the condition. For example, where there are lesions in the mouth alone, systemic drugs are less likely to be used. Where the condition is not limited to the mouth, or where there is poor response to Topical treatments, systemic drugs are more likely to be used.

Physicians can often diagnose keratosis pilaris simply by examining the skin; tests are usually not needed. However, a dermatologist can use dermoscopy to confirm the diagnosis and assess if a person with KP is responding to treatment. Physicians will often consider family history and the presence of symptoms when making the diagnosis. Those with this condition are generally encouraged to contact a physician if the bumps are bothersome and do not improve with over the counter lotions.

The diagnosis of SSSS is made clinically. This is sometimes confirmed by isolation of "S. aureus" from blood, mucous membranes, or skin biopsy; however, these are often negative. Skin biopsy may show separation of the superficial layer of the epidermis (intraepidermal separation), differentiating SSSS from TEN, wherein the separation occurs at the dermo-epidermal junction (subepidermal separation). SSSS may be difficult to distinguish from toxic epidermal necrolysis and pustular psoriasis.

In longstanding scarred lesions, squamous cell carcinoma can develop.

On diascopy, it shows characteristic "apple-jelly" color. Biopsy will reveal tuberculoid granuloma with few bacilli. Mantoux test is positive.

There are several different types of keratosis pilaris, including "keratosis pilaris rubra" (red, inflamed bumps which can be on arms, head, legs), "keratosis pilaris alba" (rough, bumpy skin with no irritation), "keratosis pilaris rubra faceii" (reddish rash on the cheeks), and related disorders. Keratosis pilaris is commonly described in association with other dry skin conditions, such as ichthyosis vulgaris, xerosis and atopic dermatitis, including those of asthma and allergies.

Keratosis pilaris does not bear any known, long-term health implications, nor is it associated with increased mortality or morbidity. It is not related to goose bumps, which results from muscle contractions, except that both occur in the area where the hair shaft exits the skin.

Pemphigus is endemic in the rural areas of Brazil, especially along inland riverbeds.

The forms of pemphigoid are considered to be connective tissue autoimmune skin diseases. There are several types:

- Gestational pemphigoid or Pemphigoid gestationis (PG) (formerly called Herpes gestationis)

- Bullous pemphigoid (BP) Rarely affect the mouth

- Mucous membrane pemphigoid, also known as Cicatricial pemphigoid (CP) (No skin involvement)

Bullous and Cicatricial pemphigoids usually affect persons who are over age 60. Gestational pemphigoid occurs during pregnancy, typically in the second or third trimester, and/or immediately following pregnancy.

Topical steroid preparations often help outbreaks; use of the weakest corticosteroid that is effective is recommended to help prevent thinning of the skin. Drugs such as antibiotics, antifungals, corticosteroids, dapsone, methotrexate, thalidomide, etretinate, cyclosporine and, most recently, intramuscular alefacept may control the disease but are ineffective for severe chronic or relapsing forms of the disease. Intracutaneous injections of botulinum toxin to inhibit perspiration may be of benefit. Maintaining a healthy weight, avoiding heat and friction of affected areas, and keeping the area clean and dry may help prevent flares.

Some have found relief in laser resurfacing that burns off the top layer of the epidermis, allowing healthy non-affected skin to regrow in its place.

Secondary bacterial, fungal and/or viral infections are common and may exacerbate an outbreak. Some people have found that outbreaks are triggered by certain foods, hormone cycles and stress.

In a few cases naltrexone appears to help.

The National Institute of Arthritis and Musculoskeletal and Skin Diseases describes it like this:

"Normally, our immune system produces antibodies that attack viruses and harmful bacteria to keep us healthy. In people with pemphigus, however, the immune system mistakenly attacks the cells in the epidermis, or top layer of the skin, and the mucous membranes. The immune system produces antibodies against proteins in the skin known as desmogleins. These proteins form the glue that keeps skin cells attached and the skin intact. When desmogleins are attacked, skin cells separate from each other and fluid can collect between the layers of skin, forming blisters that do not heal. In some cases, these blisters can cover a large area of skin."

Subcutaneous sarcoidosis (also known as "Darier–Roussy disease" and "Darier-Roussy sarcoid") is a cutaneous condition characterized by numerous 0.5- to 0.3-cm deep-seated nodules on the trunk and extremities.

Scar sarcoid (also known as "Sarcoidosis in scars") is a cutaneous condition characterized by infiltration and elevation of tattoos and old flat scars due to sarcoidosis.

Mucosal sarcoidosis is a cutaneous condition characterized by pinhead-sized papules that may be grouped and fused together to form a flat plaque.

Erythrodermic sarcoidosis is a cutaneous condition and very rare form of sarcoidosis.

The prognosis of SSSS in children is excellent, with complete resolution within 10 days of treatment, and without significant scarring. However, SSSS must be differentiated carefully from toxic epidermal necrolysis, which carries a poor prognosis. The prognosis in adults is generally much worse, and depends upon various factors such as time to treatment, host immunity, and comorbidities.