Any dermatitis may heal leaving pale skin, as may excessive use of corticosteroid creams used to treat episodes of eczema. The hypopigmentation is due to both reduced activity of melanocytes with fewer and smaller melanosomes.

The condition is most often seen in children between the ages of 3 and 16 years and is more common in males than females. However adults can also suffer from this disease.

It may occur more frequently in lighter-skinned patients, but is more apparent in those with darker complexions.

Up to a third of US school children may at some stage have this condition. Single-point prevalence studies from India have shown variable rates from 8.4%,

to 31%.

Other studies have shown prevalence rates in Brazil of 9.9%,

Egypt 13.49%,

Romania 5.1%,

Turkey 12% where higher rates were seen in those with poor socioeconomic conditions,

and just 1% in school children in Hong Kong.

This skin disease commonly affects adolescents and young adults, especially in warm and humid climates. The yeast is thought to feed on skin oils (lipids), as well as dead skin cells. Infections are more common in people who have seborrheic dermatitis, dandruff, and hyperhidrosis.

The patches of pityriasis alba may last from 1 month to about one year, but commonly on the face last a year. However it is possible that the white patches may last for more than 1 year on the face.

If the condition thickens, turns red and irritated, starts spreading, appears on other body parts, or if the baby develops thrush (fungal mouth infection), fungal ear infection (an ear infection that does not respond to antibiotics) or a persistent diaper rash, medical intervention is recommended.

Severe cases of cradle cap, especially with cracked or bleeding skin, can provide a place for bacteria to grow. If the cradle cap is caused by a fungal infection which has worsened significantly over days or weeks to allow bacterial growth (impetigo, most commonly), a combination treatment of antibiotics and antifungals may be necessary. Since it is difficult for a layperson to distinguish the difference between sebaceous gland cradle cap, fungal cradle cap, or either of these combined with a bacterial infection, medical advice should be sought if the condition appears to worsen.

Cradle cap is occasionally linked to immune disorders. If the baby is not thriving and has other problems (e.g. diarrhea), a doctor should be consulted.

In contrast to cutaneous LP, which is self limited, lichen planus lesions in the mouth may persist for many years, and tend to be difficult to treat, with relapses being common. Atrophic/erosive lichen planus is associated with a small risk of cancerous transformation, and so people with OLP tend to be monitored closely over time to detect any potential change early. Sometimes OLP can become secondarily infected with Candida organisms.

Assurances that this condition will clear as the baby matures are very common. However, studies have shown that the condition occasionally persists into the toddler years, and less commonly into later childhood. It tends to recur in adolescence and persists into adulthood. In an Australian study, about 15 percent of previously diagnosed children still had eczema 10 years later. Sometimes, cradle cap turns into atopic dermatitis. Rarely, it turns out to be misdiagnosed psoriasis.

In 2016, interferon gamma/CXCL10 axis was hypothesized to be a target for treatments that reverse inflammation. Apremilast is undergoing investigation as a potential treatment .

In most patients, the condition lasts only a matter of weeks; in some cases it can last longer (up to six months). The disease resolves completely without long-term effects. Two percent of patients have recurrence.

Types include:

- Pityriasis alba

- Pityriasis lichenoides chronica

- Pityriasis lichenoides et varioliformis acuta

- Pityriasis rosea

- Pityriasis circinata

- Pityriasis rubra pilaris

- Pityriasis versicolor

- Dandruff, historically called "Pityriasis capitis"

- Pityriasis amiantacea

The overall prevalence of PR in the United States has been estimated to be 0.13% in men and 0.14% in women. It most commonly occurs between the ages of 10 and 35. It is more common in spring.

PR is not viewed as contagious, though there have been reports of small epidemics in fraternity houses and military bases, schools and gyms.

Pityriasis lichenoides is a form of pityriasis.

Types include:

- Pityriasis lichenoides et varioliformis acuta

- Pityriasis lichenoides chronica

Pityriasis commonly refers to flaking (or scaling) of the skin. The word comes from the Greek πίτυρον "bran".

The bacteria staphylococci are present in the majority of cases. Treatment with systemic antibiotics and coal tar shampoo can completely clear the condition when Staphylococcus aureus bacteria are found. Fungal infections such as tinea capitis are known to mimic the symptoms of the condition and can be cleared with antifungal treatment.

Lichenoid trikeratosis is a cutaneous condition that may be related to keratosis lichenoides chronica.

The classification of exfoliative dermatitis into Wilson-Brocq (chronic relapsing), Hebra or pityriasis rubra (progressive), and Savill (self-limited) types may have had historical value, but it currently lacks pathophysiologic or clinical utility.

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.

It is very rare and estimated to affect 1 in 100,000 per year. Because of its rarity the documentation, cases and information are sparse and not a huge amount is known for certain, meaning that EAC could actually be a set of many un-classified skin lesions. It is known to occur at all ages and all genders equally. Some articles state that women are more likely to be affected than men.

A papulosquamous disorder is a condition which presents with both papules and scales, or both scaly papules and plaques.

Examples include psoriasis, lichen planus, and pityriasis rosea.

In cases of tinea versicolor caused by the fungus "Malassezia furfur", lightening of the skin occurs due to the fungus's production of azelaic acid, which has a slight bleaching effect.

Pityriasis lichenoides chronica (PLC) is probably caused by a hypersensitivity reaction to infectious agents such as the Epstein–Barr virus. Other infectious agents include the adenovirus and Parvovirus B19.

Often no specific cause for the eruptions is found. However, it is sometimes linked to underlying diseases and conditions such as:

- Food (including blue cheese or tomatoes).

- Contact Dermatitis (i.e. cleaning agents, fabric softeners, etc.)

- Fungal, Bacterial and Viral infections such as sinusitis, tuberculosis, candidiasis or tinea.

- Drugs including finasteride, etizolam (and benzodiazepines), chloroquine, hydroxychloroquine, oestrogen, penicillin and amitriptyline.

- Cancer (especially the type known as erythema gyratum perstans, in which there are concentric and whirling rings).

- Primary biliary cirrhosis.

- Graves disease.

- Appendicitis.

- Lupus

- Pregnancy (EAC usually disappears/stops soon after delivery of baby).

- Hormone (Contraceptive Pill, Stress, Hormone Drugs)

- Lyme Disease

The parapsoriasis groups, described and debated for nearly a century, has spawned a confusing nomenclature. There are some authors who prefer to limit the term "parapsoriasis" to large- and small-plaque variants only. However, the following classification scheme is now generally accepted:

- Large-plaque parapsoriasis

- Small-plaque parapsoriasis

- Pityriasis lichenoides

- Pityriasis lichenoides chronica

- Pityriasis lichenoides et varioliformis acuta

- Lymphomatoid papulosis

Pityriasis amiantacea (also known as "Tinea amiantacea") is an eczematous condition of the scalp in which thick tenaciously adherent scale infiltrates and surrounds the base of a group of scalp hairs. It does not result in scarring or alopecia.

Pityriasis amiantacea was first described by Alibert in 1832. Pityriasis amiantacea affects the scalp as shiny asbestos-like (amiantaceus) thick scales attached in layers to the hair shaft. The scales surround and bind down tufts of hair. The condition can be localised or covering over the entire scalp. Temporary alopecia and scarring alopecia may occur due to repeated removal of hairs attached to the scale. It is a rare disease with a female predilection.

Pityriasis amiantacea can easily be misdiagnosed due its close resemblance to other scalp diseases such as psoriasis, seborrhoeic dermatitis or lichen planus. However in pityriasis amiantacea the scales are attached to both the hair shaft and the scalp. Pityriasis amiantacea may be present with other inflammatory conditions such as atopic dermatitis or seborrhoeic dermatitis and sebaceous scales and alopecia can occur. According to the dermatology text Bolognia this condition is most often seen in psoriasis, but may also be seen in secondarily infected atopic dermatitis, seborrheic dermatitis, and tinea capitis.

Pityriasis lichenoides chronica is an uncommon, idiopathic, acquired dermatosis, characterized by evolving groups of erythematous, scaly papules that may persist for months.

PVA usually has an underlying cause, attributed to existing skin diseases and disorders associated with a cutaneous lymphoma or inflammation. Mycosis fungoides is the common lymphoma believed to cause PVA, although it may be considered a precursor when the lymphoma is (hidden) and undiagnosed. Large plaque parapsoriasis is another common causes of PVA. Less common causes include autoimmune-related connective tissue diseases such as lupus, dermatomyositis and scleroderma. Dermatoses and those that are genetically inspired, called genodermatoses, may also be an underlying cause of PVA. Among them, xeroderma pigmentosum and Rothmund-Thomson syndrome (poikiloderma congenita) are thought to be the most prominent. Ingestion of substances containing arsenic, such as arsphenamine, has also been suggested as a least common cause. PVA can also be idiopathic (of unknown cause), as seen in a small number of cases.