Plaque psoriasis 

Skin lesions are red at the base and covered by silvery scales. 

Also known as Classis Psoriasis or Psoriasis Vulgaris. The most common form of psoriasis, affecting about 80% of people with the disease. People with plaque psoriasis have raised, red, inflamed areas of skin—called plaques—often on the scalp, knees, elbows, chest, or back. These inflamed plaques of skin are covered by a silvery-white buildup called scale. It will often reoccur and its cause is not fully understood, although it is generally considered to be an autoimmune disease. 

Pustular psoriasis 

Blisters of noninfectious pus appear on the skin. Attacks of pustular psoriasis may be triggered by medications, infections, stress, or exposure to certain chemicals. 

Guttate psoriasis 

Small, teardrop shaped lesions appear on the trunk, limbs, and scalp. Guttate psoriasis is most often triggered by upper respiratory infections (for example, a sore throat caused by streptococcal bacteria). 

The second most common form of psoriasis, characterized by small, pink or red drops on the skin. This type of psoriasis may cover a large portion of the body and is usually found on the chest, back, arms, or legs. It appears after a bacterial infection such as strep throat, especially in younger patients. Some cases go away without treatment in a few weeks, while many cases are more persistent and require treatment. 

Psoriatic arthritis 

Joint and connective tissue inflammation that produces symptoms of arthritis in patients who have or will develop psoriasis. 

Inverse psoriasis (or "Flexural psoriasis")

Smooth, red patches occur in the folds of the skin near the genitals, under the breasts, or in the armpits. The symptoms may be worsened by friction, sweating and/or the presence of yeast or fungal infections. It is called inverse psoriasis because it occurs in moist areas, areas that aren't normally affected by classic psoriasis. 

Erythrodermic psoriasis 

Widespread reddening and exfoliation of the skin that may form the initial outbreak of psoriasis, but is more often the result of exacerbation of unstable plaque psoriasis, particularly under the triggering effect of: abrupt withdrawal of systemic treatment, use of systemic steroids or excessive use of high potency topical steroids corticosteroids (cortisone) or in a koebner response to a widespread allergic reaction or severe sunburn. This form of psoriasis can be genuinely dangerous, since the extreme inflammation and exfoliation interfere with the body's ability to regulate temperature and perform other barrier functions.