Psoriasis

It is an immune-mediated condition that affects the skin. It causes red, flaky, crusty patches of skin covered with silvery scales. The condition is not infectious and most people are affected only in small patches on their body. Psoriasis occurs when the immune system mistakes a normal skin cell for a pathogen, and sends out faulty signals that cause overproduction of new skin cells.

Psoriasis is not contagious . It may be classified as:

Non pustular

Psoriasis vulgaris: It is the most common form of psoriasis. It affects 80% to 90% of people with psoriasis. Plaque psoriasis typically appears as raised areas of inflamed skin covered with silvery white scaly skin. These areas are called plaques.
Psoriatic erythroderma: It involves the widespread inflammation and exfoliation of the skin over most of the body surface. It is generally accompanied by severe itching, swelling and pain. This form of psoriasis can be fatal, as the extreme inflammation and exfoliation disrupt the body’s ability to regulate temperature and for the skin to perform barrier functions
Pustular

Pustular psoriasis appears as raised bumps that are filled with noninfectious pus (pustules). Pustular psoriasis can be localized, commonly to the hands and feet (palmoplantar pustulosis), or generalised with widespread patches occurring randomly on any part of the body. Types include:

Generalized pustular psoriasis (pustular psoriasis of von Zumbusch)
Pustulosis palmaris et plantaris (persistent palmoplantar pustulosis, pustular psoriasis of the Barber type, pustular psoriasis of the extremities)
Annular pustular psoriasis
Acrodermatitis continua
Impetigo herpetiformis
Other Additional types of psoriasis include

Drug-induced psoriasis
Inverse psoriasis.
Napkin psoriasis
Seborrheic-like psoriasis

Guttate psoriasis: It is characterized by numerous small, scaly, red or pink, teardrop-shaped lesions.

Nail psoriasis: It produces a variety of changes in the appearance of finger and toe nails. These changes include discoloring under the nail plate, pitting of the nails, lines going across the nails, thickening of the skin under the nail, and the loosening (onycholysis) and crumbling of the nail.

Psoriatic arthritis: It involves joint and connective tissue inflammation. Psoriatic arthritis can affect any joint, but is most common in the joints of the fingers and toes.