Definition of Psoriasis

Psoriasis i a common, chronic skin condition in which the dermis produces keratinocytes at an accelerated rate. This causes immature keratinocytes, which are still soft, to reach the epidermis (the outer layer of the skin). The excess keratinocytes form lesions, typically scaly plaques, that itch (pruritus) or hurt.

The accelerated turnover of keratinocytes creates an immune response in the skin that dermatologists refer to as t-cell activation. The immune response produces inflammation, the body’s attempt to heal the plaques. But like the other components of psoriasis, the T-cell response is out of control and results in exacerbating, rather than relieving, the lesions.


Dermatologists believe gene mutations establish a predisposition for the accelerations that characterize psoriasis. External or environmental circumstances such as injury, infection, and stress then trigger the dysfunctions in the skin that result in the psoriasis. Psoriasis appears to run in families, suggesting that the mutated genes are inherited. Researchers continue to explore the genetic foundations of psoriasis. Once psoriasis manifests, it remains in a lifelong pattern of outbreak and remission.


Generally, dermatologists classify five types of psoriasis. Psoriasis in any of these types can also cause inflammation of the joints, a form of arthritis called psoriasic arthritis. Dermatologists may also refer to psoriasis according to the parts of the body affected, such as palmar-plantar which affects the palms of the hands and soles of the feet. About 7 million Americans have psoriasis.

Erythrodermic psoriasis

In erythrodermic psoriasis, widespread areas of the skin become red and scaly, and often swollen. This is the least common but most severe type of psoriasis. It can develop from any of the other types of psoriasis.

Flexural psoriasis

Also called inverse psoriasis, flexural psoriasis forms smooth though itchy lesions in areas such as the axillae (underarms), creases of the leg in the groin, under the breasts, and other skinfold areas. Irritation from rubbing and sweating exacerbates the lesions.

Guttate psoriasis

In guttate psoriasis, the second-most common type of psoriasis, the lesions are small and look as though they were dropped onto the skin. The lesions have raised edges with centers that are somewhat depressed and appear crumpled. Guttate psoriasis is most common on the trunk, arms, legs, and scalp. The lesions itch, and may crack and then crust over before healing. Upper respiratory infections such as colds or pharyngitis (notably strep throat) often trigger outbreaks of guttate psoriasis.

Psoriasis and Blood Donation

Some oral medications for psoriasis stay in the blood for an extended time and have the potential to cause serious birth defects. Blood banks defer people who take or who have taken these medications from donating blood for periods of time, depending on the medication. People who have taken etretinate at any time, which is no longer available, are permanently deferred because it remains in the blood indefinitely.

Plaque psoriasis

The most common form of psoriasis, plaque psoriasis features erythematous (reddened) plaques that typically develop on the knees, elbows, scalp, and trunk. The plaques itch and sometimes hurt and often crack, bleed, and crust. Plaque psoriasis also can affect the fingernails and toenails, causing pitting, deformation, discoloration, and separation from the nail bed. Emotional and physical stress (such as illness or injury) may initiate outbreaks of plaque psoriasis. Some people have few outbreaks and other people have lesions nearly continuously.

Pustular psoriasis

The lesions in pustular psoriasis look infected but simply contain fluid mixed with white blood cells, dead skin cells, and other matter that has the appearance of pus. Adverse drug reactions and topical irritants often trigger pustular psoriasis.

Symptoms and Diagnostic Path

The dermatologist diagnoses psoriasis primarily on the basis of its symptoms and history, and may choose to biopsy representative lesions to confirm. In its early stages, psoriasis may be difficult to distinguish from dermatitis and other skin disorders. The diagnosis becomes more conclusive when other family members have psoriasis.

Treatment Options and Outlook

The extent to which medical treatments can mitigate the symptoms of psoriasis depends on the type and severity of the psoriasis. Unfortunately, psoriasis responds unpredictably to treatment methods, with great individual variation. As well, the lesions may become resistant to specific treatments or medications over time, requiring a shift in therapeutic approach.

This results in a trialand-error approach that often frustrates those who have psoriasis. Dermatologists generally follow a sequential approach of progressively more intense therapy. Many people with moderate to severe psoriasis use a combination of therapies to help control their symptoms. Antibiotic medications may be necessary to treat secondary infections that affect psoriasis lesions.

Treatments for Psoriasis
Topical Medications
coal tardesonidedesoximetasone
prednisolonesalicylic acidtriamconolone
PUVA phototherapyexcimer laserultraviolet B (UVB) phototherapy
Systemic Medications
infliximabmethotrexatemycophenolate mofetil

Risk Factors and Preventive Measures

Because psoriasis has genetic predisposition, it is not possible to prevent its development. Once psoriasis manifests, it is important to receive prompt and appropriate medical treatment as well as identify and avoid triggers. Limited sun exposure, with precautions to prevent sunburn, may mitigate attacks and help the skin remain healthy.


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