There are many different types of psoriasis, often with significant overlap. They include:

• Plaque psoriasis. The most common form of psoriasis, also called psoriasis vulgaris. Marked by raised, inflamed, red lesions covered with a silvery-white buildup of dead skin cells. The nails may also be affected. According to the American Academy of Dermatology (AAD), about 80 percent of patients with psoriasis have plaque psoriasis.
  
  
• Psoriatic arthritis. Also called psoriasis arthropica or psoriatic arthropathy. This is psoriasis associated with arthritis, generally similar to rheumatoid arthritis (chronic joint inflammation). While typically milder than rheumatoid arthritis, psoriatic arthritis may be disabling. It frequently involves the fingers and toes. According to the AAD, up to 30 percent of patients with psoriasis have associated arthritis.
  
  
• Guttate psoriasis. Small, distinct, generally widespread red lesions. Onset is most common in children, particularly after respiratory infections (e.g., strep throat).
  
  
• Inverse psoriasis. Also known as skin fold psoriasis, flexural psoriasis or genital psoriasis. Smooth, dry, red lesions form in the folds of skin, commonly in the arm pits, genital area and under the breasts. This type occurs most often in patients who are overweight.
  
  
• Pustular psoriasis. Small, sterile pustules appear, dry up and form a scab. The blisters associated with this form of psoriasis are white and surrounded by red skin. They are typically localized to palms and soles. Pustular psoriasis can be very severe and may be associated with systemic symptoms (e.g., unwell feeling, fever, diarrhea). According to the AAD, pustular psoriasis affects less than 5 percent of patients with psoriasis. This type of psoriasis is particularly worsened by overindulgence of alcohol and overuse of oral steroids.
  
  
• Erythrodermic psoriasis. Also known as psoriasis universalis. This particularly severe form of psoriasis is characterized by intense redness that covers all or most of the body surface. It often causes dangerously high temperatures and a greatly increased susceptibility to infection, generally requiring hospitalization. This is the least common type of psoriasis.

When injury to the skin leads to the development of psoriasis, it is referred to as Koebner phenomenon. This may result in any type of psoriasis.