Psoriasis is a long-lasting autoimmune disease characterized by patches of abnormal skin. These skin patches are typically red, dry, itchy, and scaly. On people with darker skin the patches may be purple in colour. Psoriasis varies in severity from small, localized patches to complete body coverage."

Source : Wikipedia

Psoriasis has been frequently 'associated' with lifestyle, viral infections, bacterial infections, medications and genetic factors - but no exact 'mechanism of action' has yet been discovered,

Psoriasis is a chronic skin disease which is diagnosed in approximately 1–3% of the general population and is not only characterised by skin lesions but also affects the whole body. Aetiopathogenesis remains unknown; however, genetic, environmental and immunological factors are believed to play a role in the development of the disease The unknown cause and pathogenesis are the reasons for the lack of an effective treatment and final cure."

Source : Dermatology and Therapy,13, pp. 1617–1627 (2023)

New research (2023 - linked above) suggests research for a possible link with a metabolic process known as thekynurenine pathway

Also see : Eczemaplugin-autotooltip__plain plugin-autotooltip_bigEczema

The most common form (percentage needed) of Eczema is 'Atopic Eczema' - in this case 'atopic' meaning 'of unknown origin'.

It can occur anywhere on the body, but is common on the hands, elbows, knees, face and scalp.

A variety of factors, including environmental, dietary, genetic, viral, and bacterial, are known to be associated with the disorder. But no direct biological mechanism which explains the persistent skin outbreaks has yet been found. and Psoriatic Arthritis (PsA)plugin-autotooltip__plain plugin-autotooltip_bigPsoriatic Arthritis (PsA)

"Psoriatic arthritis, in short called PsA, is a rheumatologic disease that effects about 1,5 million Americans. About one in three people with the skin disease psoriasis, will get psoriatic arthritis. It affects the joints as well as the tendons, and it may also affect the spine.