Psoriasis is a chronic skin condition that affects approximately 7.5 million Americans, according to the National Psoriasis Foundation. Doctors classify psoriasis into five different types based on the appearance of the skin lesions and if the condition affects any other part of the body. Because many other skin problems cause lesions similar to that of psoriasis on areas of the body similar to psoriasis, doctors often have difficulty diagnosing the correct condition.
Cause
Although classified as a skin disease, psoriasis actually occurs due to an abnormal response of the immune system, according to the American Osteopathic College of Dermatology. In those who suffer from psoriasis, the T-cells---a specific type of white blood cell---become overstimulated and signal the skin cells to heal injuries that are not present by speeding up their rate of growth. This causes the formation of red, inflamed skin and lesions that appear white and scaly due to the build-up of skin cells. Other skin conditions, including some types of eczema, also involve an overactive immune system that triggers the skin cells to form red, scaly patches.
Flare-Ups
Patients with psoriasis experience periods of time when the skin appears normal followed by periods with active lesions. Psoriasis flare-ups may be triggered by stress, injury to the skin, certain types of medications, exposure to allergens or infections with bacteria such as streptococcus. Eczema, a general term used to describe skin conditions involving inflammation, irritation and itchiness, also causes flare-ups that may be triggered by allergens, skin irritants, a fluctuation in temperatures, skin injury and stress. The cyclic nature of both skin diseases can make it difficult to distinguish between them.
Location
Psoriasis can affect the skin in any part of the body, including the eyelids, ears, mouth, lips and skin folds. Because it commonly affects the skin on the hands and the soles of the feet, it can resemble other conditions. Reiter's syndrome, also known as reactive arthritis, describes an inflammatory condition that causes skin lesions on the palms of the hands and soles of the feet that look similar to psoriasis, according to MedLine Plus. A condition known as palmoplantar pustulosis causes tiny, fluid-filled blisters on the palms of the hands and soles of the feet. Similarly, one form of psoriasis known as pustular psoriasis causes white, noninfectious blisters to form, usually in localized areas of the body such as the hands and feet.
Appearance
The skin lesions caused by psoriasis vary depending on the type of psoriasis. Plaque psoriasis, the most common form, causes red, inflamed, raised patches of skin covered by white scaly skin. Atopic dermatitis, the most common form of eczema, causes red, itchy and scaly patches of skin that often appear red, especially when scratched. Both conditions commonly affect the elbows and knees. Guttate psoriasis causes small, red individual spots on the trunk, arms and legs that appear similar to rashes caused by diseases such as chicken pox.
Other Affected Areas
Approximately 30 percent of all patients with psoriasis develop psoriatic arthritis, a condition that causes pain, stiffness and swelling in and around the joints, according to the National Psoriasis Foundation. The symptoms of psoriatic arthritis, including joint pain, morning stiffness, back pain, fatigue and eye redness, appear similar to the symptoms of reactive arthritis, which both produce skin blisters on the hands and feet.
